Wheel identifying apparatus and tire inflation pressure detecting apparatus with function of wheel identification

ABSTRACT

A wheel identifying apparatus according to the present invention includes a plurality of transceivers, a triggering device, a receiver, and a wheel identifier. Each of the transceivers is located on one of a plurality of wheels of a vehicle and works to receive a trigger signal and transmit a response signal in response to receipt of the trigger signal. The triggering device is located on a body of the vehicle at different distances from the transceivers and works to transmit the trigger signal. The receiver works to receive the response signals transmitted by the transceivers. The wheel identifier is operatively connected to the receiver and works to identify, for each of the response signals received by the receiver, the wheel on which the transceiver having transmitted the response signal is located using the fact that strengths of the trigger signal at the transceivers are different from each other.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based on and claims priority from Japanese PatentApplications No. 2005-197497, filed on Jul. 6, 2005, and No.2005-198703, filed on Jul. 7, 2005, the contents of which are herebyincorporated by reference into this application.

BACKGROUND OF THE INVENTION

1. Technical Field of the Invention

The present invention relates generally to tire inflation pressuredetecting apparatuses for detecting the inflation pressure of tires on avehicle and tire location detecting apparatuses for automaticallydetecting the locations of tires on a vehicle.

More particularly, the invention relates to a direct-type tire inflationpressure detecting apparatus which has a function of wheelidentification.

2. Description of the Related Art

Conventional direct-type tire inflation pressure detecting apparatusesgenerally include a plurality of transmitters and a receiver.

Each of the transmitters is directly mounted on one of a plurality ofwheels of a vehicle and includes a pressure sensor working to sense theinflation pressure of a tire fitted on the wheel. Each of thetransmitters is configured to transmit a pressure signal representativeof the inflation pressure of the tire sensed by the pressure sensor.

The receiver is mounted on the body of the vehicle and includes at leastone antenna. The receiver is configured to receive the pressure signalstransmitted from the transmitters via the antenna and determine theinflation pressure of the tires based on the received pressure signals.

In the above arrangement, in addition to the pressure signalstransmitted by the transmitters, the receiver may also receive pressuresignals transmitted by external transmitters. However, it is impossiblefor the receiver to determine whether a pressure signal received therebyhas been transmitted by one of the transmitters or by an externaltransmitter. Moreover, it is also impossible for the receiver to detectthe locations of the transmitters (i.e., the tires) on the vehicle. Inother words, the receiver cannot identify the wheel on which thetransmitter having transmitted a pressure signal and the tire whoseinflation pressure is indicated by the pressure signal are located.

To solve the above problems, as disclosed in U.S. Pat. No. 5,602,524,each of the transmitters may be configured to transmit an identificationsignal (to be referred to as ID signal hereinafter) representative ofthe identification thereof along with the pressure signal. On the otherhand, the receiver may be configured to have reference ID signalsregistered therein, each of which coincides with the ID signal of one ofthe transmitters and is associated with the location of thattransmitter.

Thus, the receiver may work to compare an ID signal received therebywith the reference ID signals registered therein and identify thetransmitter which has transmitted the ID signal when the ID signalcoincides with one of the reference ID signals.

Consequently, the receiver can identify the wheel on which theidentified transmitter is mounted. More specifically, the receiver candetermine whether the wheel is a FR (front-right), a FL (front-left), aRR (rear-right), or a RL (rear-left) wheel of the vehicle. Further, thereceiver can determine the inflation pressure of the tire fitted on theidentified wheel based on the pressure signal received along with the IDsignal.

However, with the above configuration, it is required to previouslyregister the ID signals specific to the respective transmitters asreference ID signals in the receiver through associating the ID signalswith the locations of the respective transmitters on the vehicle (i.e.,the wheels on which the respective transmitters are mounted). Moreover,as tire replacement or rotations are performed, it is required to updatethe reference ID signals in the receiver.

However, the registration of the ID signals in the receiver is atime-consuming task, and thus it is desired to automatically perform theregistration task. Further, for automatically performing theregistration task, it is desired to automatically detect the locationsof the transmitters (or the associated tires), in other words, toautomatically identify the wheel on which each of the transmitters (orthe associated tires) is located.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above-mentionedproblems.

It is, therefore, an object of the present invention to provide a wheelidentifying apparatus for a vehicle which can automatically andaccurately identify, for each of the transmitters (or transceivers), thewheel on which it is located without performing the time-consuming IDsignal registration task.

It is a further object of the present invention to provide a wheelidentifying apparatus for a vehicle which can automatically andaccurately identify, for each of the transmitters (or transceivers), thewheel on which it is located without using any ID signals.

It is a still further object of the present invention to provide a tireinflation pressure detecting apparatus for a vehicle which canautomatically and accurately detect the locations as well as theinflation pressure of tires on the vehicle.

According to the present invention, there is provided a wheelidentifying apparatus which includes:

a first and a second transceiver which are respectively located on afirst and a second wheel of a vehicle, each of the transceivers workingto receive a trigger signal and transmit a response signal in responseto receipt of the trigger signal;

a triggering device working to transmit the trigger signal, thetriggering device being located on a body of the vehicle at differentdistances from the transceivers, so that strengths of the trigger signalat the transceivers are different from each other;

a receiver working to receive the response signals transmitted by thetransceivers; and

a wheel identifier operatively connected to the receiver, the wheelidentifier working to identify, for each of the response signalsreceived by the receiver, the wheel on which the transceiver havingtransmitted the response signal is located.

According to an implementation of the invention, the wheel identifyingapparatus is configured such that:

upon receipt of the trigger signal transmitted by the triggering device,each of the transceivers determines the strength of the trigger signalthereat and transmits the response signal which conveys signal strengthinformation indicative of the determined strength of the trigger signal,and

the wheel identifier identifies, for each of the response signalsreceived by the receiver, the wheel on which the transceiver havingtransmitted the response signal is located based on the signal strengthinformation conveyed by the response signal.

According to another implementation of the invention, the wheelidentifying apparatus is configured such that:

upon receipt of the trigger signal transmitted by the triggering device,each of the transceivers determines the strength of the trigger signalthereat, determines a transmission time according to the determinedstrength of the trigger signal, and transmits the response signal at thedetermined transmission time,

the receiver receives the response signals transmitted by thetransceivers at different reception times, and

the wheel identifier identifies, for each of the response signalsreceived by the receiver, the wheel on which the transceiver havingtransmitted the response signal is located based on the reception timeat which the response signal is received by the receiver.

According to yet another implementation of the invention, the wheelidentifying apparatus is configured such that:

each of the transceivers has a variable receiver sensitivity andreceives the trigger signal transmitted by the triggering device with ahigher value of the receiver sensitivity,

in response to receipt of the trigger signal, each of the transceiverschanges the receiver sensitivity thereof from the higher value to alower value,

after transmission of the trigger signal, the triggering device furthertransmits a check signal,

each of the transceivers determines a receiving behavior thereof inreception of the check signal with the lower value of the receiversensitivity,

each of the transceivers transmits the response signal which conveysreceiving behavior information indicative of the determined receivingbehavior, and

the wheel identifier identifies, for each of the response signalsreceived by the receiver, the wheel on which the transceiver havingtransmitted the response signal is located based on the receivingbehavior information conveyed by the response signal.

According to still another implementation of the invention, the wheelidentifying apparatus is configured such that:

each of the transceivers has a variable receiver sensitivity andreceives the trigger signal transmitted by the triggering device with ahigher value of the receiver sensitivity,

in response to receipt of the trigger signal, each of the transceiverschanges the receiver sensitivity thereof from the higher value to alower value,

after transmission of the trigger signal, the triggering device furthertransmits a check signal,

each of the transceivers determines a receiving behavior thereof inreception of the check signal with the lower value of the receiversensitivity,

each of the transceivers determines a transmission time according to thedetermined receiving behavior and transmits the response signal at thedetermined transmission time,

the receiver receives the response signals transmitted by thetransceivers at different reception times, and

the wheel identifier identifies, for each of the response signalsreceived by the receiver, the wheel on which the transceiver havingtransmitted the response signal is located based on the reception timeat which the response signal is received by the receiver.

Further, according to the present invention, there is provided a tireinflation pressure detecting apparatus which includes:

a first and a second pressure sensor which are respectively located on afirst and a second wheel of a vehicle, each of the pressure sensorsworking to sense inflation pressure of an associated one of tires fittedon the first and second wheels and output tire pressure informationindicative of the sensed inflation pressure of the associated tire;

a first and a second transceiver which are respectively located on thefirst and second wheels of the vehicle, each of the transceivers workingto receive a trigger signal and transmit a response signal, whichconveys the tire pressure information outputted by an associated one ofthe first and second pressure sensors, in response to receipt of thetrigger signal;

a triggering device working to transmit the trigger signal, thetriggering device being located on a body of the vehicle at differentdistances from the transceivers, so that strengths of the trigger signalat the transceivers are different from each other;

a receiver working to receive the response signals transmitted by thetransceivers;

a wheel identifier operatively connected to the receiver, the wheelidentifier working to identify, for each of the response signalsreceived by the receiver, the wheel on which the transceiver havingtransmitted the response signal is located; and

a tire pressure determiner operatively connected to the receiver and thewheel identifier, the tire pressure determiner working to determine, foreach of the response signals received by the receiver, the inflationpressure of the tire that is located on the same wheel as thetransceiver having transmitted the response signal based on the tirepressure information conveyed by the response signal.

According to an implementation of the invention, the tire inflationpressure detecting apparatus is configured such that:

upon receipt of the trigger signal transmitted by the triggering device,each of the transceivers determines the strength of the trigger signalthereat and transmits the response signal which conveys signal strengthinformation indicative of the determined strength of the trigger signalas well as the tire pressure information, and

the wheel identifier identifies, for each of the response signalsreceived by the receiver, the wheel on which the transceiver havingtransmitted the response signal is located based on the signal strengthinformation conveyed by the response signal.

According to another implementation of the invention, the tire inflationpressure detecting apparatus is configured such that:

upon receipt of the trigger signal transmitted by the triggering device,each of the transceivers determines the strength of the trigger signalthereat, determines a transmission time according to the determinedstrength of the trigger signal, and transmits the response signal at thedetermined transmission time,

the receiver receives the response signals transmitted by thetransceivers at different reception times, and

the wheel identifier identifies, for each of the response signalsreceived by the receiver, the wheel on which the transceiver havingtransmitted the response signal is located based on the reception timeat which the response signal is received by the receiver.

According to yet another implementation of the invention, the tireinflation pressure detecting apparatus is configured such that:

each of the transceivers has a variable receiver sensitivity andreceives the trigger signal transmitted by the triggering device with ahigher value of the receiver sensitivity,

in response to receipt of the trigger signal, each of the transceiverschanges the receiver sensitivity thereof from the higher value to alower value,

after transmission of the trigger signal, the triggering device furthertransmits a check signal,

each of the transceivers determines a receiving behavior thereof inreception of the check signal with the lower value of the receiversensitivity,

each of the transceivers transmits the response signal which conveysreceiving behavior information indicative of the determined receivingbehavior as well as the tire pressure information, and

the wheel identifier identifies, for each of the response signalsreceived by the receiver, the wheel on which the transceiver havingtransmitted the response signal is located based on the receivingbehavior information conveyed by the response signal.

According to still another implementation of the invention, the tireinflation pressure detecting apparatus is configured such that:

each of the transceivers has a variable receiver sensitivity andreceives the trigger signal transmitted by the triggering device with ahigher value of the receiver sensitivity,

in response to receipt of the trigger signal, each of the transceiverschanges the receiver sensitivity thereof from the higher value to alower value,

after transmission of the trigger signal, the triggering device furthertransmits a check signal,

each of the transceivers determines a receiving behavior thereof inreception of the check signal with the lower value of the receiversensitivity,

each of the transceivers determines a transmission time according to thedetermined receiving behavior and transmits the response signal at thedetermined transmission time,

the receiver receives the response signals transmitted by thetransceivers at different reception times, and

the wheel identifier identifies, for each of the response signalsreceived by the receiver, the wheel on which the transceiver havingtransmitted the response signal is located based on the reception timeat which the response signal is received by the receiver.

Consequently, through providing the above wheel identifying apparatusand the tire inflation pressure detecting apparatus, the objects of thepresent invention are achieved.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood more fully from the detaileddescription given hereinafter and from the accompanying drawings of thepreferred embodiments of the invention, which, however, should not betaken to limit the invention to the specific embodiments but are for thepurpose of explanation and understanding only.

In the accompanying drawings:

FIG. 1 is a schematic view showing the overall configuration of a tireinflation pressure detecting apparatus according to the first embodimentof the invention;

FIG. 2A is a functional block diagram showing the configuration of eachof transceivers of the tire inflation pressure detecting apparatus ofFIG. 1;

FIG. 2B is a functional block diagram showing the configuration of areceiver of the tire inflation pressure detecting apparatus of FIG. 1;

FIG. 3 is a graphical representation illustrating the attenuationcharacteristic of strength of a trigger signal, in a free space, withdistance from a triggering device which transmits the trigger signal;

FIG. 4 is an application of FIG. 3 to the tire inflation pressuredetecting apparatus of FIG. 1;

FIG. 5 is a schematic view illustrating an example of the wheelidentification process of the tire inflation pressure detectingapparatus of FIG. 1;

FIG. 6 is a time chart illustrating the transmission timings for atrigger signal and frames in the tire inflation pressure detectingapparatus of FIG. 1;

FIG. 7 is an application of FIG. 3 to a tire inflation pressuredetecting apparatus according to the second embodiment of the invention;

FIG. 8 is a schematic view illustrating an example of the wheelidentification process of the tire inflation pressure detectingapparatus according to the second embodiment of the invention;

FIG. 9 is a schematic view showing the overall configuration of a tireinflation pressure detecting apparatus according to the third embodimentof the invention;

FIG. 10A is an application of FIG. 3 to the tire inflation pressuredetecting apparatus of FIG. 9;

FIG. 10B is another application of FIG. 3 to the tire inflation pressuredetecting apparatus of FIG. 9;

FIG. 11 is a schematic view illustrating an example of the wheelidentification process of the tire inflation pressure detectingapparatus of FIG. 9;

FIG. 12 is a schematic view showing the overall configuration of a tireinflation pressure detecting apparatus according to the fifth embodimentof the invention;

FIG. 13A is a functional block diagram showing the configuration of eachof transceivers of the tire inflation pressure detecting apparatus ofFIG. 12;

FIG. 13B is a functional block diagram showing the configuration of areceiver of the tire inflation pressure detecting apparatus of FIG. 12;

FIG. 14 is a flow chart showing a process of the receiver of the tireinflation pressure detecting apparatus of FIG. 12;

FIG. 15 is a flow chart showing a process of each of the transceivers ofthe tire inflation pressure detecting apparatus of FIG. 12;

FIG. 16 is a time chart illustrating the wheel identification process ofthe tire inflation pressure detecting apparatus of FIG. 12;

FIG. 17 is a functional block diagram showing the configuration of eachof transceivers of a tire inflation pressure detecting apparatusaccording to the sixth embodiment of the invention;

FIG. 18 is a flow chart showing a process of a receiver of the tireinflation pressure detecting apparatus according to the sixth embodimentof the invention;

FIG. 19 is a flow chart showing a process of each of the transceivers ofthe tire inflation pressure detecting apparatus according to the sixthembodiment of the invention; and

FIG. 20 is a time chart illustrating the wheel identification process ofthe tire inflation pressure detecting apparatus according to the sixthembodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments of the present invention will be describedhereinafter with reference to FIGS. 1-20.

It should be noted that, for the sake of clarity and understanding,identical components having identical functions in different embodimentsof the invention have been marked, where possible, with the samereference numerals in each of the figures.

First Embodiment

FIG. 1 shows the overall configuration of a tire inflation pressuredetecting apparatus S1 according the first embodiment of the invention.

The tire inflation pressure detecting apparatus S1 is installed to avehicle 1 and configured to detect the inflation pressure of four tireseach of which is fitted on one of four wheels 6 a-6 d of the vehicle 1(i.e., the FR wheel 6 a, the FL wheel 6 b, the RR wheel 6 c, and the RLwheel 6 d).

As shown in FIG. 1, the tire inflation pressure detecting apparatus S1includes four transceivers 2, a receiver 3, a warning device 4, and atriggering device 5.

Each of the transceivers 2 is mounted on one of the four wheels 6 a-6 d,so as to have association with the tire on the one of the wheels 6 a-6d.

Each transceiver 2 works to sense the inflation pressure of theassociated tire and transmit a frame that contains tire pressureinformation indicative of the sensed inflation pressure of theassociated tire.

Referring to FIG. 2A, each transceiver 2 is configured with a sensingunit 21, a microcomputer 22, a battery 23, a transmitting antenna 24,and a receiving antenna 25.

The sensing unit 21 is configured with sensors, such as a diaphragm-typepressure sensor and a temperature sensor, and works to output signalsrepresentative of the sensed inflation pressure of the tire and thesensed temperature of air in the tire.

The microcomputer 22 is of a well-known type and functionally includes acontrolling unit 22 a, a transmitting unit 22 b, and a receiving unit 22c. The microcomputer 22 is configured to implement predeterminedprocesses in accordance with a program installed in a memory (not shown)of the controlling unit 22 a.

The controlling unit 22 a works to receive the signals outputted fromthe sensing unit 21 and process those signals. The controlling unit 22 aalso works to assemble the frame, which contains the tire pressureinformation indicative of the inflation pressure of the tire sensed bythe sensing unit 21, and provide the frame to the transmitting unit 22b.

Further, the controlling unit 22 a works to receive, via the receivingantenna 25 and the receiving unit 22 c, a trigger signal transmitted bythe triggering device 5 and determine the strength of the receivedtrigger signal through signal processing thereof. The controlling unit22 a also works to store, in the frame or another frame, signal strengthinformation indicative of the determined strength.

Furthermore, the controlling unit 22 a works to control the transmittingunit 22 b to transmit the frame.

The transmitting unit 22 b works to transmit, via the transmittingantenna 24, the frame provided by the controlling unit 22 a to thereceiver 3.

The receiving unit 22 c works to receive, via the receiving antenna 25,the trigger signal transmitted by the triggering device 5 and providethe received trigger signal to the controlling unit 22 a.

The battery 23 is provided to supply electrical power necessary foroperation of the other units.

The above-described transceivers 2 each are fixed to an air valve of anassociated one of the wheels 6 a-6 d of the vehicle 1 and at least thesensing unit 21 thereof is placed inside the tire on the wheel so as tobe exposed to the air within the tire.

On the other hand, the receiver 3 is mounted on the body 7 of thevehicle 1. The receiver 3 works to receive all the frames transmitted bythe transceivers 2 and determine the inflation pressure of the fourtires based on the tire pressure information contained in the receivedframes. The receiver 3 also works to identify, for each of the receivedframes, the wheel on which the transceiver 2 having transmitted theframe is mounted.

Referring to FIG. 2B, the receiver 3 is configured with a receivingantenna 31 and a microcomputer 32.

The receiving antenna 31 is fixed to the body 7 of the vehicle 1 toreceive, as illustrated in FIG. 1, all the frames transmitted by thefour transceivers 2.

The microcomputer 32 is of a well-known type and functionally includes areceiving unit 32 a and a controlling unit 32 b. The microcomputer 32 isconfigured to implement predetermined processes, based on the signalscontained in the frames transmitted from the transceivers 2, inaccordance with a program installed in a memory (not shown) of thecontrolling unit 32 b.

The receiving unit 32 a works to receive, via the receiving antenna 31,all the frames transmitted by the transceivers 2 and provide thereceived frames to the controlling unit 32 b.

The controlling unit 32 b works to output a command signal to thetriggering device 5 for causing the triggering device 5 to transmit thetrigger signal. The controlling unit 32 b also works to identify, foreach of the frames received from the receiving unit 32 a, the wheel onwhich the transceiver 2 having transmitted the frame is mounted.

The controlling unit 32 b further works to determine, for each of theframes received from the receiving unit 32 a, the inflation pressure ofthe tire that is located on the same wheel as the transceiver 2 havingtransmitted the frame based on the tire pressure information containedin the frame.

Thus, both the inflation pressure and location of each of the four tirescan be determined by the controlling unit 32 b. When the determinedinflation pressure of any of the four tires is decreased to below apredetermined threshold Th, the controlling unit 32 b outputs a warningsignal indicative of both the decreased inflation pressure and locationof the tire.

The warning device 4 is, as illustrated in FIG. 1, electricallyconnected to the receiver 3 and arranged in a location visible for thedriver of the vehicle 1. The warning device 4 is configured with, forexample, a warning display on the instrument panel of the vehicle 1. Thewarning device 4 works to inform, in response to receipt of the warningsignal from the receiver 3, the driver of both the decreased inflationpressure and location of the tire.

The triggering device 5 works to transmit, in response to receipt of thecommand signal from the receiver 3, the trigger signal withpredetermined strength. The triggering device 5 is arranged on the body7 of the vehicle 1 at different distances from the wheels 6 a-6 d, sothat the strengths of the trigger signal at the transceivers 2 aredifferent from each other. For example, in the present embodiment, thetriggering device 5 is arranged, as illustrated in FIG. 1, in closevicinity to the RL wheel 6 d of the vehicle 1. Thus, the distances fromthe triggering device 5 to the wheels 6 a-6 d increase in the order ofthe RL wheel 6 d, the RR wheel 6 c, the FL wheel 6 b, and the FR wheel 6a.

In addition, it is preferable for the triggering device 5 to be arrangedin such a location that no metal member covers the triggering device 5and it is possible to protect the triggering device 5 from foreignmatters, such water and a stone, during running of the vehicle 1.Further, it is also preferable for the triggering device 5 to bearranged in such a location that the differences among the distancesfrom the triggering device 5 to the wheels 6 a-6 d are large. Forexample, the triggering device 5 may be arranged on the rear side of theRR wheel 6 c and the RL wheel 6D or on the front side of the FR wheel 6a and the FL wheel 6 b.

After having described the overall configuration of the tire inflationpressure detecting apparatus S1, operation thereof will be describedhereinafter.

According to the present embodiment, the tire inflation pressuredetecting apparatus S1 has two different operation modes. The first modeis “ID registration mode” and the second one is “tire pressure detectionmode”. The tire inflation pressure detecting apparatus S1 is configuredto operate in the ID registration mode first and then in the tirepressure detection mode.

Specifically, when an ignition switch (not shown) of the vehicle 1 isturned from off to on, the receiver 3 and the triggering device 5 aresupplied with electric power from a battery (not shown) on the vehicle1, thus entering the ID registration mode.

Then, the controlling unit 32 b of the receiver 3 outputs the commandsignal to the triggering device 5. In response to receipt of the commandsignal, the triggering device 5 transmits the trigger signal with thepredetermined strength to each of the transceivers 2.

Upon receiving the trigger signal via the receiving antenna 25 and thereceiving unit 22 c, the controlling unit 22 a of each of thetransceivers 2 is activated to determine the strength of the triggersignal thereat.

It is easy to understand that the strength of the trigger signalattenuates with increase in the distance from the triggering device 5.FIG. 3 illustrates the attenuation characteristic of strength of atrigger signal in a free space with distance from a triggering devicewhich transmits the trigger signal. FIG. 4 illustrates an application ofFIG. 3 to the tire inflation pressure detecting apparatus S1.

Specifically, as described above, the distances from the triggeringdevice 5 to the wheels 6 a-6 d increase in the order of the RL wheel 6d, the RR wheel 6 c, the FL wheel 6 b, and the FR wheel 6 a.Accordingly, the strengths of the trigger signal at the associatedtransceivers 2 decrease in the order of the RL wheel 6 d, the RR wheel 6c, the FL wheel 6 b, and the FR wheel 6 a.

After determining the strength of the trigger signal thereat, thecontrolling unit 22 a of each of the transceivers 2 stores in the framethe signal strength information indicative of the determined strength ofthe trigger signal and ID information indicative of the identificationof the transceiver 2. Then, the controlling unit 22 a sets a waitingtime and controls the transmitting unit 22 b to transmit the frame afterelapse of the waiting time from receipt of the trigger signal.

In addition, the waiting time may be set randomly, so as to allow allthe transceivers 2 to transmit the respective frames at different times,thereby avoiding interference of the frames at the receiver 3.

Upon receipt of all the frames transmitted by the transceivers 2, thecontrolling unit 32 b of the receiver 3 retrieves the signal strengthinformation and ID information contained in the frames. Then, thecontrolling unit 32 b orders the frames in the descending order of thestrengths of the trigger signal indicated by the signal strengthinformation contained in the frames.

Through the ordering, the controlling unit 32 b identifies thetransceiver 2 which has transmitted the frame containing the signalstrength information indicative of the maximum strength as being mountedon the RL wheel 6 d, that which has transmitted the frame containing thesignal strength information indicative of the secondary strength asbeing mounted on the RR wheel 6 c, that which has transmitted the framecontaining the signal strength information indicative of the thirdstrength as being mounted on the FL 6 b, and that which has transmittedthe frame containing the signal strength information indicative of theminimum strength as being mounted on the RR wheel.

More specifically, referring to FIG. 5, where the four transceivers 2are respectively designated with their identifications A, B, C, and D,the strengths of the trigger signal at the transceivers A-D aredifferent from each other. For example, the strengths of the triggersignal at the transceivers A-D are 10, 55, 34, and 20, respectively.

Referring further to FIG. 6, for transmission of the frames, the waitingtimes may be set to be in inverse proportion to the strengths of thetrigger signal. For example, a maximum waiting time may be set for thetransceiver A at which the strength of the trigger signal is minimum, sothat the transceiver A transmits the frame at the last. Consequently,the transceivers A-D transmit the respective frames at different times,thus avoiding interference of the frames at the receiver 3.

Upon receipt of the frames transmitted by the transceivers A-D, thecontrolling unit 32 b of the receivers 3 orders the transceivers A-D (inother words, orders the respective frames) in the descending order ofthe strengths of the trigger signal thereat, thus resulting in the orderof B, C, D, and A.

Through the ordering, controlling unit 32 b identifies, for each of thetransceivers A-D, the wheel on which it is mounted. Consequently, thetransceiver B is identified as being mounted on the RL wheel 6 d, thetransceiver C is identified as being mounted on the RR wheel 6 c, thetransceiver D is identified as being mounted on the FL wheel 6 b, andthe transceiver A is identified as being mounted on the FR wheel 6 a.

After the wheel identification, the controlling unit 32 b of thereceiver 3 registers in the memory thereof the ID information containedin the received frames as reference ID information associated with therespective identified wheels.

Then, the operation of the tire inflation pressure detecting apparatusS1 is shifted from the ID registration mode to the tire pressuredetection mode.

In the tire pressure detection mode, the controlling unit 22 a of eachof the transceivers 2 receives the signals outputted from the sensingunit 21 and processes those signals. Then, the controlling unit 22 astores in the frame the tire pressure information indicative of theinflation pressure of the associated tire sensed by the sensing unit 21along with the ID information indicative of the identification of thetransceiver 2. Further, the controlling unit 22 a controls thetransmitting unit 22 b to repeatedly transmit the frame at predeterminedtime intervals (e.g., one minute).

The controlling unit 32 b of the receiver 3 receives all the framestransmitted by the transceivers 2 via the receiving antenna 31 and thereceiving unit 32 a.

Then, the controlling unit 32 b identifies, for each of the receivedframes, the wheel on which the transceiver 2 having transmitted theframe is mounted through comparison of the ID information contained inthe frame with all the reference ID information registered in thememory.

Further, the controlling unit 32 b determines, for each of the receivedframes, the inflation pressure of the tire that is located on the samewheel as the transceiver 2 having transmitted the frame based on thetire pressure information contained in the frame.

In addition, each of the frames transmitted by the transceivers 2 maycontain tire temperature information indicative of the temperature ofair within the associated tire, so that the controlling unit 32 b of thereceiver 3 can perform, if necessary, temperature compensation for thedetermined inflation pressure of the tires based on the temperatureinformation contained in the respective received frames.

Consequently, both the inflation pressure and location of each of thefour tires are determined by the controlling unit 32 b. When thedetermined inflation pressure of any of the four tires is decreased tobelow the predetermined threshold Th, the controlling unit 32 b informs,via the warning device 4, the driver of both the decreased inflationpressure and location of the tire.

When the ignition switch of the vehicle 1 is turned from on to off, thecontrolling unit 32 b of the receivers 3 transmits again the commandsignal, causing the triggering device 5 to transmit the trigger signal.Upon receiving the trigger signal via the receiving antenna 25 and thereceiving unit 22 c, the controlling unit 22 a of each of thetransceivers 2 is deactivated, thus completing the entire operation ofthe tire inflation pressure detecting apparatus S1.

The above-described tire inflation pressure detecting apparatus S1according to the present embodiment has the following advantages.

In the tire inflation pressure detecting apparatus S1, the triggeringdevice 5 is arranged on the body 7 of the vehicle 1 at differentdistances from the wheels 6 a-6 d, thus making the strengths of thetrigger signal at the transceivers 2 different from each other; each ofthe transceivers 2 transmits the frame containing the signal strengthinformation indicative of the strength of the trigger signal at thetransceiver 2; the receiver 3 identifies, for each of the framesreceived from the transceivers 2, the wheel on which the transceiver 2having transmitted the frame is mounted based on the signal strengthinformation contained in the frame.

With the above configuration, it is possible for the receiver 3 toaccurately determine the locations of the transceivers 2 on the vehicle1.

Accordingly, with the above configuration, it is possible for the tireinflation pressure detecting apparatus S1 to automatically andaccurately detect the locations as well as the inflation pressure of thetires on the vehicle 1.

Further, with the above configuration, it is possible for the tireinflation pressure detecting apparatus S1 to automatically and reliablyperform the ID information registration task.

Furthermore, it is possible for all the transceivers 2 to have the sameconfiguration and for the receiver 3 to include only the singlereceiving antenna 31, thus decreasing the manufacturing cost of the tireinflation pressure detecting apparatus S1.

In addition, in the present embodiment, the tire inflation pressuredetecting apparatus SI is configured to operate in the two differentmodes, i.e., the ID registration mode and the tire pressure detectionmode.

However, the tire inflation pressure detecting apparatus S1 may also beconfigured to operate only in a single mode in which: each of thetransceivers 2 repeatedly transmits, at the predetermined timeintervals, the frame that contains the tire pressure informationindicative of the inflation pressure of the associated tire and thesignal strength information indicative of the strength of the triggersignal at the transceiver 2; the receiver 3 identifies, for each of theframes received from the transceivers 2, the wheel on which thetransceiver 2 having transmitted the frame is mounted based on thesignal strength information contained in the frame; the receiver 3further determines, for each of the frames received from thetransceivers 2, the inflation pressure of the tire that is located onthe same wheel as the transceiver 2 having transmitted the frame basedon the tire pressure information contained in the frame.

With such a modified configuration, it is possible to automatically andaccurately detect the locations as well as the inflation pressure of thetires on the vehicle 1 without using any ID information.

Second Embodiment

This embodiment illustrates a tire inflation pressure detectingapparatus S2 which has almost the same configuration as the tireinflation pressure detecting apparatus S1 according to the previousembodiment. Accordingly, only the differences therebetween will bedescribed hereinafter.

In the previous embodiment, each of the four transceivers 2 receives thetrigger signal transmitted by the triggering device 5 and transmits theframe containing the signal strength information indicative of thestrength of the trigger signal at the transceiver 2; the receiver 3identifies, for each of the frames received from the four transceivers2, the wheel on which the transceiver 2 having transmitted the frame ismounted based on the signal strength information contained in the frame.

In comparison, in the present embodiment, the triggering device 5outputs the trigger signal with a limited strength, so that one of thefour transceivers 2 cannot receive the trigger signal.

Specifically, in some practical cases, the output strength of thetrigger signal is limited due to regulations. Consequently, asillustrated in FIG. 7, the strength of the trigger signal at thetransceiver 2 on the FR wheel 6 a becomes lower than a lower limit ofstrength under which the transceiver 2 cannot detect the trigger signal.

The other three transceivers 2 that can receive the trigger signaloperate in the same way as in the previous embodiment.

For example, referring to FIG. 8, the strengths of the trigger signal atthe three transceivers B-C are 55, 34, and 20, respectively.

In the ID registration mode, each of the three transceivers 2 transmitsthe frame that contains the signal strength information indicative ofthe strength of the trigger signal at the transceiver 2 and the IDinformation indicative of the identification of the transceiver 2.

Upon receipt of the frames transmitted by the transceivers B-D, thecontrolling unit 32 b of the receivers 3 orders the transceivers B-D (inother words, orders the respective frames) in the descending order ofthe strengths of the trigger signal thereat, thus resulting in the orderof B, C, and D.

Through the ordering, controlling unit 32 b identifies, for each of thetransceivers B-D, the wheel on which it is mounted. Consequently, thetransceiver B is identified as being mounted on the RL wheel 6 d, thetransceiver C is identified as being mounted on the RR wheel 6 c, andthe transceiver D is identified as being mounted on the FL wheel 6 b.

After the wheel identification, the controlling unit 32 b of thereceiver 3 stores in the memory thereof the ID information indicative ofthe identifications B-D as the reference ID information associated withthe respective identified wheels 6 b-6 d.

In the tire pressure detection mode, after the first receipt of theframes transmitted by all the transceivers 2, the controlling unit 32 bof the receiver 3 further identifies, for the one of the frames whichcontains unregistered ID information indicative of the identification A,the wheel on which the transceiver 2 having transmitted the one of theframes is mounted as the FR wheel 6 a. In other words, the controllingunit 32 b identifies the transceiver A as being mounted on the FR wheel6 a.

Then, the controlling unit 32 b of the receiver 3 registers in thememory thereof the ID information indicative of the identification A asthe reference ID information associated with the FR wheel 6 a.

The rest of operation of the tire inflation pressure detecting apparatusS2 is the same as that of the tire inflation pressure detectingapparatus S1 according to the previous embodiment; therefore, thedescription thereof is omitted here.

The tire inflation pressure detecting apparatus S2 according to thepresent embodiment has the same advantages as the tire inflationpressure detecting apparatus S1 according to the previous embodiment.Further, the tire inflation pressure detecting apparatus S2 has anadditional advantage of being capable of accurately determining thelocations of the transceivers 2 and thus those of the associated tireseven when the output strength of the trigger signal is limited.

In addition, in the present embodiment, it is impossible for thereceiver 3 to activate and deactivate the transceiver 2 on the FR wheel6 a via the trigger signal. Then, other methods may be used instead,such as configuring the transceivers 2 to include a motion sensor forsensing rotation of the associated tire and to be self-activated andself-deactivated based on the sensed rotation.

Third Embodiment

This embodiment illustrates a tire inflation pressure detectingapparatus S3 which has almost the same configuration as the tireinflation pressure detecting apparatus S1 according to the firstembodiment. Accordingly, only the differences therebetween will bedescribed hereinafter.

In the first embodiment, there is provided only the single triggeringdevice 5 in the tire inflation pressure detecting apparatus S1. Further,the trigger signal transmitted by the triggering device 5 is received byall the transceivers 2.

In comparison, with reference to FIG. 9, there are provided twotriggering devices 5 a and 5 b in the tire inflation pressure detectingapparatus S3. Further, the trigger signal transmitted by each of thetriggering devices 5 a and 5 b is received by only three of thetransceivers 2.

Specifically, as shown in FIG. 9, the triggering device 5 a is arrangedin close vicinity to the RL wheel 6 d, while the triggering device 5 bis arranged in close vicinity to the FL wheel 6 b. Consequently, boththe triggering devices 5 a and 5 b are positioned on the left side ofthe longitudinal centerline C-C of the vehicle 1 at different distancesfrom the wheels 6 a-6 d.

With the above arrangement, in the ID registration mode, the controllingunit 32 b of the receiver 3 first outputs the command signal to one ofthe two triggering devices, for example, the triggering device 5 a, thuscausing the triggering device 5 a to transmit the trigger signal.

As in the first embodiment, the strengths of the trigger signaltransmitted by the triggering device 5 a at the transceivers 2 aredifferent from each other. Specifically, the strengths of the triggersignal transmitted by the triggering device 5 a at the transceivers 2,which are respectively mounted on the wheels 6 a-6 d, decrease in theorder of the RL wheel 6 d, the RR wheel 6 c, the FL wheel 6 b, and theFR wheel 6 a.

Thus, as shown in FIG. 10A, when the trigger signal is outputted by thetriggering device 5 a with the limited strength as in the secondembodiment, the strength of the trigger signal at the transceiver 2 onthe FR wheel 6 a becomes lower than the lower limit of strength, so thatthe transceiver 2 on the FR wheel 6 a cannot detect the trigger signal.

Further, since the difference between the distances from the triggeringdevice 5 a to the RR wheel 6 c and the FL wheel 6 b is small, thedifference between the strengths of the trigger signal at thetransceivers 2 on the wheels 6 c ant 6 b is accordingly small.Consequently, in some practically cases, it may be difficult for thecontrolling unit 32 b of the receiver 3 to distinguish the framesreceived from the transceivers 2 on the wheels 6 c and 6 b from oneanother based on the strengths of the trigger signal thereat.

In consideration of the above, in the present embodiment, thecontrolling unit 32 b of the receiver 3 further outputs the commandsignal to the other of the two triggering devices, i.e., the triggeringdevice 5 b, thus causing the triggering device 5 b to transmit thetrigger signal.

Similar to the case of the trigger signal transmitted by the triggeringdevice 5 a, the strengths of the trigger signal transmitted by thetriggering device 5 b at the transceivers 2 are different from eachother. Specifically, the strengths of the trigger signal transmitted bythe triggering device 5 b at the transceivers 2, which are respectivelymounted on the wheels 6 a-6 d, decrease in the order of the FL wheel 6b, the FR wheel 6 a, the RL wheel 6 d, and the RR wheel 6 c.

Thus, as shown in FIG. 10B, when the trigger signal is outputted by thetriggering device 5 b with the limited strength, the strength of thetrigger signal at the transceiver 2 on the RR wheel 6 c becomes lowerthan the lower limit of strength, so that the transceiver 2 on the RRwheel 6 c cannot detect the trigger signal.

Further, since the difference between the distances from the triggeringdevice 5 b to the FR wheel 6 a and the RL wheel 6 d is small, thedifference between the strengths of the trigger signal at thetransceivers 2 on the wheels 6 a ant 6 d is accordingly small.Consequently, in some practical cases, it may be difficult for thecontrolling unit 32 b of the receiver 3 to distinguish the framesreceived from the transceivers 2 on the wheels 6 a and 6 d from oneanother based on the strengths of the trigger signal transmitted by thetriggering device 5 b thereat.

Accordingly, in the present embodiment, the controlling unit 32 b of thereceiver 3 identifies the locations of the transceivers 2 in threestages.

Specifically, in the first stage, the controlling unit 32 b receives theframes that are transmitted by the transceivers 2 on the wheels 6 d, 6c, and 6 b in response to receipt of the trigger signal transmitted bythe triggering device 5 a. Then, the controlling unit 32 b identifiesthe transceiver 2 which has transmitted the frame containing the signalstrength information indicative of the maximum strength as being mountedon the RL wheel 6 d, and the other two transceivers 2 as being mountedon the RR wheel 6 c or the FL wheel 6 b.

In the second stage, the controlling unit 32 b receives the frames thatare transmitted by the transceivers 2 on the wheels 6 b, 6 a, and 6 d inresponse to receipt of the trigger signal transmitted by the triggeringdevice 5 b. Then, the controlling unit 32 b identifies the transceiver 2which has transmitted the frame containing the signal strengthinformation indicative of the maximum strength as being mounted on theFL wheel 6 b, and the other two transceivers 2 as being mounted on theFR wheel 6 a or the RL wheel 6 d.

In the third stage, the controlling unit 32 b identifies the remainingunidentified transceivers 2. Specifically, among the two transceivers 2that have been identified as being mounted on the RR wheel 6 c or the FLwheel 6 b in the first stage, since one of them has been identified asbeing mounted on the FL wheel 6 b in the second stage, the other isaccordingly identified as being mounted on the RR wheel 6 c. Similarly,among the two transceivers 2 that have been identified as being mountedon the FR wheel 6 a or the RL wheel 6 d in the second stage, since oneof them has been identified as being mounted on the RL wheel 6 d in thefirst stage, the other is accordingly identified as being mounted on theFR wheel 6 a.

Consequently, the locations of all the transceivers 2 on the vehicle 1are identified by the controlling unit 32 b of the receiver 3.

FIG. 11 illustrates an example of the above-described wheelidentification process, where the transceivers 2 are respectivelydesignated with their identifications A-D.

As shown in FIG. 11, the trigger signal transmitted by the triggeringdevice 5 a is received by the three transceivers C, D, and A and thestrengths of the trigger signal thereat are 55, 10, and 11,respectively.

Accordingly, in the first stage of the wheel identification process, thecontrolling unit 32 b of the receiver 3 identifies the transceiver Cwhich has the maximum strength of 55 as being mounted on the RL wheel 6d, and the other two transceivers D and A as being mounted on the RRwheel 6 c or the FL wheel 6 b.

Further, the trigger signal transmitted by the triggering device 5 b isreceived by the three transceivers A, B, and C and the strengths of thetrigger signal thereat are 55, 10, and 13, respectively.

Accordingly, in the second stage of the wheel identification process,the controlling unit 32 b of the receiver 3 identifies the transceiver Awhich has the maximum strength of 55 as being mounted on the FL wheel 6b, and the other two transceivers B and C as being mounted on the FRwheel 6 a or the RL wheel 6 d.

In the third stage of the wheel identification process, the controllingunit 32 b of the receiver 3 identifies the transceiver D as beingmounted on the RR wheel 6 c and the transceiver B as being mounted onthe FR wheel 6 a.

The tire inflation pressure detecting apparatus S3 according to thepresent embodiment has the same advantages as the tire inflationpressure detecting apparatus S1 according to the first embodiment.Further, the tire inflation pressure detecting apparatus S3 has anadditional advantage of being capable of accurately determining thelocations of the transceivers 2 and thus those of the associated tireseven when the output strength of the trigger signal is limited.

In addition, in the present embodiment, it is assumed that the triggersignal transmitted by each of the triggering devices 5 a and 5 b isreceivable by only three of the transceivers 2. However, even in thecase that the trigger signal is receivable by only two of thetransceivers 2, it is still possible for the receiver 3 to accuratelyand easily determine the locations of the transceivers 2. Such a casemay happen when the triggering devices 5 a and 5 b transmit therespective trigger signals with more limited strength or thetransceivers 2 each have a lower receiver sensitivity.

Fourth Embodiment

This embodiment illustrates a tire inflation pressure detectingapparatus S4 which has almost the same configuration as the tireinflation pressure detecting apparatus S1 according to the firstembodiment. Accordingly, only the differences therebetween will bedescribed hereinafter.

In the first embodiment, each of the transceivers 2 receives the triggersignal transmitted by the triggering device 5 and transmits the framecontaining the signal strength information indicative of the strength ofthe trigger signal at the transceiver 2; the receiver 3 identifies, foreach of the frames received from the transceivers 2, the wheel on whichthe transceiver 2 having transmitted the frame is mounted based on thesignal strength information contained in the frame.

In comparison, in the present embodiment, the transceivers 2 receive thetrigger signal transmitted by the triggering device 5 and transmit therespective frames at different transmission times according to thestrengths of the trigger signal thereat; the receiver 3 thus receivesthe frames transmitted from the transceivers 2 at different receptiontimes and identifies, for each of the received frames, the wheel onwhich the transceiver 2 having transmitted the frame is mounted based onthe reception time at which the frame is received.

Specifically, upon receiving the trigger signal via the receivingantenna 25 and the receiving unit 22 c, the controlling unit 22 a ofeach of the transceivers 2 is activated to determine the strength of thetrigger signal thereat.

Then, the controlling unit 22 a determines a transmission time accordingto the determined strength of the trigger signal. For example, thetransmission time may be determined by using a map stored in the memoryof the controlling unit 22 a and representing a predefined relationshipbetween the strength of the trigger signal and the transmission time orcalculated as a function of the strength of the trigger signal.

Since the strengths of the trigger signal at the transceivers 2 aredifferent from each other, the transmission times determined by thecontrolling units 22 a of the transceivers 2 are accordingly differentfrom each other.

After assembly of the frame that contains the ID information, thecontrolling unit 22 a of each of the transceivers 2 transmits the frameat the determined transmission time.

Thus, the receiver 3 receives all the frames transmitted by thetransceivers 2 at different reception times.

Then, the controlling unit 32 b of the receiver 3 identifies, for eachof the received frames, the wheel on which the transceiver 2 havingtransmitted the frame is mounted based on the reception time at whichthe frame is received.

For example, the controlling unit 32 b may order the received framesaccording to the order of the reception times at which the frames arereceived, and then determines the locations of the transceivers 2 havingtransmitted the frames through matching the order of the frames with anorder of the wheels 6 a-6 d which are made according to the distancesfrom the triggering device 5 to the wheels 6 a-6 d. Otherwise, thecontrolling unit 32 b may store in the memory thereof the same map orthe same function stored in the transceivers 2, inversely determine thestrengths of the trigger signal at the transceivers 2 based on thereception times at which the respective frames from the transceivers 2are received, and determine the locations of the transceivers 2 based onthe determined strengths of the trigger signal thereat.

The rest of operation of the tire inflation pressure detecting apparatusS4 is the same as that of the tire inflation pressure detectingapparatus S1 according to the first embodiment; therefore, thedescription thereof is omitted here.

The tire inflation pressure detecting apparatus S4 according to thepresent embodiment has the same advantages as the tire inflationpressure detecting apparatus S1 according to the first embodiment.

Fifth Embodiment

FIG. 12 shows the overall configuration of a tire inflation pressuredetecting apparatus S5 according to the fifth embodiment of theinvention. In the figure, the tire inflation pressure detectingapparatus S5 is installed to the vehicle 1 and configured to detect theinflation pressure of the four tires which are respectively fitted onthe four wheels 6 a-6 d of the vehicle 1 (i.e., the FR wheel 6 a, the FLwheel 6 b, the RR wheel 6 c, and the RL wheel 6 d).

As shown in FIG. 12, the tire inflation pressure detecting apparatus S5includes four transceivers 2, a receiver 3, a warning device 4, and twotriggering devices 5 a and 5 b.

Each of the transceivers 2 is mounted on one of the four wheels 6 a-6 d,so as to have association with the tire on the one of the wheels 6 a-6d.

Each transceiver 2 works to sense the inflation pressure of theassociated tire and transmit a frame that contains tire pressureinformation indicative of the sensed inflation pressure of theassociated tire.

Referring to FIG. 13A, each transceiver 2 is configured with a sensingunit 21, a microcomputer 22, a battery 23, a transmitting antenna 24,and a receiving antenna 25.

The sensing unit 21 is configured with sensors, such as a diaphragm-typepressure sensor and a temperature sensor, and works to output signalsrepresentative of the sensed inflation pressure of the tire and thesensed temperature of air in the tire.

The microcomputer 22 is of a well-known type and functionally includes acontrolling unit 22 a, a transmitting unit 22 b, and a receiving unit 22c. The microcomputer 22 is configured to implement predeterminedprocesses in accordance with a program installed in a memory (not shown)of the controlling unit 22 a.

The controlling unit 22 a works to receive the signals outputted fromthe sensing unit 21 and process those signals. The controlling unit 22 aalso works to assemble the frame, which contains the tire pressureinformation indicative of the inflation pressure of the tire sensed bythe sensing unit 21, and provide the frame to the transmitting unit 22b.

Further, the controlling unit 22 a works to receive, via the receivingantenna 25 and the receiving unit 22 c, a trigger signal transmitted byone of the triggering devices 5 a and 5 b and output a sensitivity-downcommand signal to the receiving antenna 25 in response to receipt of thetrigger signal. The sensitivity-down command signal indicates aninstruction for the receiving antenna 25 to change the receiversensitivity thereof from a higher value to a lower value.

With the lower value of the receiver sensitivity of the receivingantenna 25, when a check signal is transmitted by the one of thetriggering devices 5 a and 5 b following the transmission of the triggersignal, the controlling unit 22 a can or cannot detect the check signaldepending on the distance from the transceiver 2 to the one of thetriggering devices 5 a and 5 b. In other words, with the lower value ofthe receiver sensitivity, the receiving behavior of the transceiver 2 inreception of the check signal is dependant on the distance from thetransceiver 2 to the one of the triggering device 5 a and 5 b.

The controlling unit 22 a further works to make a response to thetransmission of the check signal by the one of the triggering devices 5a and 5 b according to the receiving behavior of the transceiver 2 inreception of the check signal.

Specifically, in the present embodiment, the controlling unit 22 a worksto check whether the check signal is received thereby with the lowervalue of the receiver sensitivity of the receiving antenna 25, determinea transmission time according to the result of the check, and controlthe transmitting unit 22 b to transmit, at the determined transmissiontime, the frame which conveys receiving behavior information indicativeof the receiving behavior of the transceiver 2 in reception of the checksignal. More specifically, in this case, the receiving behavior of thetransceiver 2 is represented by the result of the check on whether thecheck signal is received by the transceiver 2 with the lower value ofthe receiver sensitivity.

The transmitting unit 22 b works to transmit, via the transmittingantenna 24, the frame provided by the controlling unit 22 a to thereceiver 3.

The receiving unit 22 c works to receive, via the receiving antenna 25,the trigger signal transmitted by one of the triggering devices 5 a and5 b and provide the received trigger signal to the controlling unit 22a.

The battery 23 is provided to supply electrical power necessary foroperation of the other units.

The receiving antenna 25 is configured with an antenna element 25 a, areceiver sensitivity switch 25 b, and a damping resistor 25 c. Theantenna element 25 a is capable of receiving an electromagnetic wavethat has a low frequency (e.g., 125 kHz). The receiver sensitivityswitch 25 b and the damping resistor 25 c are connected in series witheach other. Further, the serially connected receiver sensitivity switch25 b and damping resistor 25 c are together connected in parallel withthe antenna element 25 a.

With such a configuration, when the receiver sensitivity switch 25 b isoff and the damping resistor 25 c is thus electrically separated fromthe antenna element 25 a, the receiver sensitivity of the receivingantenna 25 has the higher value. However, when the sensitivity-downcommand signal is outputted from the controlling unit 22 a to thereceiving antenna 25, the receiver sensitivity switch 25 b is turnedfrom off to on, thus bring the damping resistor 25 c into parallelelectrical connection with the antenna element 25 a. As a result, thereceiver sensitivity of the receiving antenna 25 is changed from thehigher value to the lower value.

The above-described transceivers 2 each are fixed to an air valve of anassociated one of the wheels 6 a-6 d of the vehicle 1 and at least thesensing unit 21 thereof is placed inside the tire on the wheel so as tobe exposed to the air within the tire.

On the other hand, the receiver 3 is mounted on the body 7 of thevehicle 1. The receiver 3 works to receive all the frames transmitted bythe transceivers 2 and determine the inflation pressure of the fourtires based on the tire pressure information contained in the receivedframes. The receiver 3 also works to identify, for each of the receivedframes, the wheel on which the transceiver 2 having transmitted theframe is mounted.

Referring to FIG. 13B, the receiver 3 is configured with a receivingantenna 31 and a microcomputer 32.

The receiving antenna 31 is fixed to the body 7 of the vehicle 1 toreceive, as illustrated in FIG. 12, all the frames transmitted by thefour transceivers 2.

The microcomputer 32 is of a well-known type and functionally includes areceiving unit 32 a and a controlling unit 32 b. The microcomputer 32 isconfigured to implement predetermined processes, based on the signalscontained in the frames transmitted from the transceivers 2, inaccordance with a program installed in a memory (not shown) of thecontrolling unit 32 b.

The receiving unit 32 a works to receive, via the receiving antenna 31,all the frames transmitted by the transceivers 2 and provide thereceived frames to the controlling unit 32 b.

The controlling unit 32 b works to output a first command signal forcausing the triggering devices 5 a and 5 b to transmit the triggersignal and a second command signal for causing the same to transmit thecheck signal. The controlling unit 32 b also works to identify, for eachof the frames received from the receiving unit 32 a, the wheel on whichthe transceiver 2 having transmitted the frame is mounted.

The controlling unit 32 b further works to determine, for each of theframes received from the receiving unit 32 a, the inflation pressure ofthe tire that is located on the same wheel as the transceiver 2 havingtransmitted the frame based on the tire pressure information containedin the frame.

Thus, both the inflation pressure and location of each of the four tirescan be determined by the controlling unit 32 b. When the determinedinflation pressure of any of the four tires is decreased to below thepredetermined threshold Th, the controlling unit 32 b outputs a warningsignal indicative of both the decreased inflation pressure and locationof the tire.

The warning device 4 is, as illustrated in FIG. 12, electricallyconnected to the receiver 3 and arranged in a location visible for thedriver of the vehicle 1. The warning device 4 is configured with, forexample, a warning display on the instrument panel of the vehicle 1. Thewarning device 4 works to inform, in response to receipt of the warningsignal from the receiver 3, the driver of the decreased inflationpressure and location of the tire.

The triggering devices 5 a and 5 b each work to transmit the triggersignal with predetermined strength in response to receipt of the firstcommand signal from the receiver 3 and to transmit the check signal withthe same strength in response to receipt of the second command signalfrom the receiver 3.

The triggering device 5 a is arranged on the body 7 of the vehicle 1such that it is closer to the front wheels 6 a and 6 b than the rearwheels 6 c and 6 d and at different distances from the FR wheel 6 a andthe FL wheel 6 b. Consequently, the strengths of the check signaltransmitted by the triggering device 5 a at the transceivers 2 aredifferent from each other. On the other hand, the triggering device 5 bis arranged on the body 7 of the vehicle 1 such that it is closer to therear wheels 6 c and 6 d than the front wheels 6 a and 6 b and atdifferent distances from the RR wheel 6 c and the RL wheel 6 d.Consequently, the strengths of the check signal transmitted by thetriggering device 5 b at the transceivers 2 are also different from eachother.

Further, in the present embodiment, the triggering devices 5 a and 5 bare positioned on the same side (i.e., the right side) of thelongitudinal centerline C-C of the vehicle 1. Accordingly, thetriggering device 5 a is closer to the FR wheel 6 a than the FL wheel 6b, and the triggering device 5 b is closer to the RR wheel 6 c than theRL wheel 6 d.

In addition, it is preferable for the triggering devices 5 a and 5 b tobe arranged in such locations that no metal members cover the triggeringdevices 5 a and 5 b and it is possible to protect the triggering devices5 a and 5 b from foreign matters, such water and a stone, during runningof the vehicle 1.

After having described the overall configuration of the tire inflationpressure detecting apparatus S5, operation thereof will be describedhereinafter with reference to FIGS. 14 and 15, which respectivelyillustrate the processes of the receiver 3 and the transceivers 2 duringthe operation.

According to the present embodiment, the tire inflation pressuredetecting apparatus S5 has two different operation modes. The first modeis “ID registration mode” and the second one is “tire pressure detectionmode”. The tire inflation pressure detecting apparatus S5 is configuredto operate in the ID registration mode first and then in the tirepressure detection mode.

Specifically, when the ignition switch of the vehicle 1 is turned fromoff to on, the receiver 3 and the triggering devices 5 a and 5 b aresupplied with electric power from the battery on the vehicle 1, thusentering the ID registration mode.

Then, the receiver 3 outputs the first command signal to the triggeringdevice 5 a, as indicated at the step 100 in FIG. 14.

In response to receipt of the first command signal, the triggeringdevice 5 a transmits the trigger signal with the predetermined strengthto the transceivers 2.

On the other hand, each of the transceivers 2 checks whether the triggersignal is received thereby, as indicated at the step 200 of FIG. 15.

If the check at the step 200 results in a “NO” answer, then the processdirectly goes to the end.

Otherwise, if the check at the step 200 results in a “YES” answer, theprocess proceeds to the step 205.

Since the receiver sensitivity of each of the transceivers 2 has thehigher value at this stage, the trigger signal that is transmitted bythe triggering device 5 a with the predetermined strength is received byboth the transceivers 2 on the front wheels 6 a and 6 b, and thus theprocesses in those transceivers 2 proceed to the step 205.

At the step 205, the receiver sensitivity of each of the transceivers 2is changed from the higher value to the lower value in response toreceipt of the trigger signal.

At the step 210, a parameter Nr, which represents the number of receiptsof the check signal, is set to zero; at the step 215, the count Tc of atimer in the controlling unit 22 a is also set to zero.

Next, the receiver 3 outputs, after a first predetermined time periodfrom the output of the first command signal, the second command signalto the triggering device 5 a, as indicated at the step 105 in FIG. 14.

In response to receipt of the second command signal, the triggeringdevice 5 a transmits the check signal with the predetermined strength tothe transceivers 2.

Turning to FIG. 15, each of the transceivers 2 on the front wheels 6 aand 6 b checks whether the check signal transmitted from the triggeringdevice 5 a is received thereby, as indicated at the step 220.

As described previously, the strength of the check signal attenuateswith increase in the distance from the triggering device 5 a.Accordingly, the strength of the check signal at the transceiver 2 onthe FR wheel 6 a is higher than that at the transceiver 2 on the FLwheel 6 b. Consequently, with the lower values of the receiversensitivities, the transceiver 2 on the FR wheel 6 a can receive thecheck signal, while the transceiver 2 on the FL wheel 6 b cannot.

Thus, for the transceiver 2 on the FR wheel 6 a, the check at the step220 results in a “YES” answer; the process then proceeds to the step225.

At the step 225, the parameter Nr is increased by 1, and the processthen proceeds to the step 230.

On the other hand, for the transceiver 2 on the FL wheel 6 b, the checkat the step 220 results in a “NO” answer; the process then directly goesto the step 230.

At the step 230, a check is made on whether the count TC of the timer isover a predetermined standby time Ts, in other words, whether thepresent time instant is within a second predetermined time period fromthe receipt of the trigger signal.

The predetermined standby time Ts (or the second predetermined timeperiod) may be set to have a constant value (e.g., 0.1 second) or avarying value. For example, the predetermined standby time Ts may be setto vary according to various vehicle or tire conditions, such as thevehicle speed and the inflation pressure of the tires. However, in anycase, the predetermined standby time Ts must be longer than or equal tothe sum of the first predetermined time period and a time required forthe receiver 3 to complete the transmission of the check signal.

If the check at the step 230 results in a “NO” answer, then the processreturns to the step 220.

Otherwise, if the check at the step 230 results in a “YES” answer, thenthe process proceeds to the step 235.

At the step 235, a further check is made on whether the parameter Nr isequal to 1, in other words, whether the check signal is received by theindividual transceiver 2.

For the transceiver 2 on the FR wheel 6 a, the check at the step 235results in a “YES” answer; the process then proceeds to the step 240.

At the step 240, the transceiver 2 transmits the frame that conveys IDinformation indicative of the identification of the transceiver 2 andthe receiving behavior information indicative of the result of the checkat the step 235, i.e., the presence of receipt of the check signal bythe transceiver 2. Then, the process goes to the end.

On the other hand, for the transceiver 2 on the FL wheel 6 b, the checkat the step 235 results in a “NO” answer; the process then proceeds tothe step 245.

At the step 245, a waiting time Tw is set and the transceiver 2 waitsfor the set waiting time Tw.

Through arrangement of the step 245, it is possible to avoidinterference of the frames transmitted by the different transceivers 2at the receiver 3.

At the succeeding step 250, the transceiver 2 transmits the frame thatconveys ID information indicative of the identification of thetransceiver 2 and the receiving behavior information indicative of theresult of the check at the step 235, i.e., the absence of receipt of thecheck signal by the transceiver 2. Then, the process goes to the end.

Turning back to FIG. 14, the receiver 3 makes a check on whether theframes transmitted by the transceivers 2 on the front wheels 6 a and 6 bare received thereby, as indicated at the step 110.

If the check at the step 110 results in a “NO” answer, then the processreturns to the step 100.

Otherwise, the check at the step 110 results in a “YES” answer, then theprocess proceeds to the step 115.

At the step 115, the receiver 3 identifies, for the one of the framesreceived thereby which contains the receiving behavior informationindicative of the presence of receipt of the check signal, the wheel onwhich the transceiver 2 having transmitted the frame is mounted as theFR wheel 6 a. Then, the receiver 3 stores in the memory thereof the IDinformation contained in the frame as reference ID informationassociated with the FR wheel 6 a.

At the step 120, the receiver 3 further identifies, for the other of theframes received thereby which contains the receiving behaviorinformation indicative of the absence of receipt of the check signal,the wheel on which the transceiver 2 having transmitted the frame ismounted as the FL wheel 6 b. Then, the receiver 3 stores in the memorythereof the ID information contained in the frame as reference IDinformation associated with the FL wheel 6 b.

At the succeeding steps 125-135, the receiver 3 performs, with respectto the transceivers 2 on the rear wheels 6 c and 6 d, the same processas at the steps 100-110, by sequentially outputting the first and secondcommand signals to the triggering device 5 b. Meanwhile, thetransceivers 2 on the rear wheels 6 c and 6 d perform, as thetransceivers 2 on the front wheels 6 a and 6 b, the process indicated inFIG. 15.

At the step 140, the receiver 3 identifies, for the one of the newlyreceived frames which contains the receiving behavior informationindicative of the presence of receipt of the check signal, the wheel onwhich the transceiver 2 having transmitted the frame is mounted as theRR wheel 6 c. Then, the receiver 3 stores in the memory thereof the IDinformation contained in the frame as reference ID informationassociated with the RR wheel 6 c.

At the step 145, the receiver 3 further identifies, for the other of thenewly received frames which contains the receiving behavior informationindicative of the absence of receipt of the check signal, the wheel onwhich the transceiver 2 having transmitted the frame is mounted as theRL wheel 6 d. Then, the receiver 3 stores in the memory thereof the IDinformation contained in the frame as reference ID informationassociated with the RL wheel 6 d. Then, the process goes to the end.

Thus, the receiver 3 has identified, for each of all the frames receivedthereby, the wheel on which the transceiver 2 having transmitted theframe is mounted based on the receiving behavior information containedin the frame.

The above-described wheel identification process may be understood morefully from FIG. 16.

As shown in FIG. 16, after the ignition switch (IG) of the vehicle 1 isturned from off to on, the triggering device 5 a sequentially transmitsthe trigger signal (T. S.) and the check signal (C. S.).

Then, the transceiver 2 on the FR wheel 6 a receives both the triggersignal and the check signal transmitted by the triggering device 5 a andtransmits the frame after elapse of the predetermined standby time Ts(or after the second predetermined time period) from the receipt of thetrigger signal.

In comparison, the transceiver 2 on the FL wheel 6 b receives only thetrigger signal transmitted by the triggering device 5 a and transmitsthe frame after elapse of a time equal to the sum of the predeterminedstandby time Ts and the waiting time Tw from the receipt of the triggersignal.

Thereafter, the triggering device 5 b sequentially transmits the triggersignal and the check signal.

Then, the transceiver 2 on the RR wheel 6 c receives both the triggersignal and the check signal transmitted by the triggering device 5 b andtransmits the frame after elapse of the predetermined standby time Tsfrom the receipt of the trigger signal.

In comparison, the transceiver 2 on the RL wheel 6 d receives only thetrigger signal transmitted by the triggering device 5 b and transmitsthe frame after elapse of a time equal to the sum of the predeterminedstandby time Ts and the waiting time Tw from the receipt of the triggersignal.

After completion of the wheel identification process, the operation ofthe tire inflation pressure detecting apparatus S5 is shifted from theID registration mode to the tire pressure detection mode.

In the tire pressure detection mode, the controlling unit 22 a of eachof the transceivers 2 receives the signals outputted from the sensingunit 21 and processes those signals. Then, the controlling unit 22 astores in the frame the tire pressure information indicative of theinflation pressure of the associated tire sensed by the sensing unit 21along with the ID information indicative of the identification of thetransceiver 2. Further, the controlling unit 22 a controls thetransmitting unit 22 b to repeatedly transmit the frame at predeterminedtime intervals (e.g., one minute).

The controlling unit 32 b of the receiver 3 receives all the framestransmitted by the transceivers 2 via the receiving antenna 31 and thereceiving unit 32 a.

Then, the controlling unit 32 b identifies, for each of the receivedframes, the wheel on which the transceiver 2 having transmitted theframe is mounted through comparison of the ID information contained inthe frame with all the reference ID information registered in thememory.

Further, the controlling unit 32 b determines, for each of the receivedframes, the inflation pressure of the tire that is located on the samewheel as the transceiver 2 having transmitted the frame based on thetire pressure information contained in the frame.

Additionally, each of the frames transmitted by the transceivers 2 maycontain tire temperature information indicative of the temperature ofair within the associated tire, so that the controlling unit 32 b of thereceiver 3 can perform, if necessary, temperature compensation for thedetermined inflation pressure of the tires based on the temperatureinformation contained in the respective received frames.

Consequently, both the inflation pressure and location of each of thefour tires are determined by the controlling unit 32 b. When thedetermined inflation pressure of any of the four tires is decreased tobelow the predetermined threshold Th, the controlling unit 32 b informs,via the warning device 4, the driver of both the decreased inflationpressure and location of the tire.

To sum up, in the tire inflation pressure detecting apparatus S5according to the present embodiment, the triggering device 5 a islocated at different distances from the transceivers 2 on the frontwheels 6 a and 6 b and the triggering device 5 b is located at differentdistances from the transceivers 2 on the rear wheels 6 c and 6 d; eachof the transceivers 2 has the variable receiver sensitivity and changesthe receiver sensitivity from the higher value to the lower value inresponse to receipt of the trigger signal transmitted by thecorresponding one of the triggering devices 5 a and 5 b; with the lowervalues of the receiver sensitivities, there are differences between thereceiving behaviors of the transceivers 2 in reception of the checksignal transmitted by the corresponding ones of the triggering devices 5a and 5 b; the receiver 3 identifies, for each of the frames receivedthereby, the wheel on which the transceiver 2 having transmitted theframe is mounted based on the receiving behavior information containedin the frame.

With the above configuration, it is possible for the receiver 3 toaccurately determine the locations of the transceivers 2 on the vehicle1.

Accordingly, with the above configuration, it is possible for the tireinflation pressure detecting apparatus S5 to automatically andaccurately detect the locations as well as the inflation pressure of thetires on the vehicle 1.

Further, with the above configuration, it is possible for the tireinflation pressure detecting apparatus S5 to automatically and reliablyperform the ID information registration task.

Furthermore, it is possible for all the transceivers 2 to have the sameconfiguration and for the receiver 3 to include only the singlereceiving antenna 31, thus decreasing the manufacturing cost of the tireinflation pressure detecting apparatus S5.

In addition, the above configuration of the tire inflation pressuredetecting apparatus S5 may be modified such that: the transceivers 2transmit the respective frames which does not contain receiving behaviorinformation at different transmission times according to the receivingbehaviors thereof in reception of the check signal transmitted by thecorresponding ones of the triggering devices 5 a and 5 b; the receiver 3thus receives all the frames transmitted by the transceivers 2 atdifferent reception times and identifies, for each of the receivedframes, the wheel on which the transceiver 2 having transmitted theframe is mounted based on the reception time at which the frame isreceived.

Moreover, in the present embodiment, the tire inflation pressuredetecting apparatus S5 is configured to operate in the two differentmodes, i.e., the ID registration mode and the tire pressure detectionmode.

However, the tire inflation pressure detecting apparatus S5 may also beconfigured to operate only in a single mode in which: each of thetransceivers 2 repeatedly transmits, at the predetermined timeintervals, the frame that contains the tire pressure informationindicative of the inflation pressure of the associated tire and thereceiving behavior information indicative of the receiving behavior ofthe transceiver 2 in reception of the check signal; the receiver 3identifies, for each of the frames received from the transceivers 2, thewheel on which the transceiver 2 having transmitted the frame is mountedbased on the receiving behavior information contained in the frame; thereceiver 3 further determines, for each of the frames received from thetransceivers 2, the inflation pressure of the tire that is located onthe same wheel as the transceiver 2 having transmitted the frame basedon the tire pressure information contained in the frame.

With such a modified configuration, it is possible to automatically andaccurately detect the locations as well as the inflation pressure of thetires on the vehicle 1 without using any ID information.

Sixth Embodiment

This embodiment illustrates a tire inflation pressure detectingapparatus S6 which has almost the same configuration as the tireinflation pressure detecting apparatus S5 according to the previousembodiment. Accordingly, only the differences therebetween will bedescribed hereinafter.

In the previous embodiment, each of the triggering devices 5 a and 5 btransmits the trigger signal first and the check signal after thepredetermined first time period from the transmission of the triggersignal.

In comparison, in the present embodiment, each of the triggering devices5 a and 5 b consecutively transmits the trigger signal and a continuouscarrier which follows the trigger signal.

FIG. 17 shows the configuration of each of the transceivers 2 in thetire inflation pressure detecting apparatus S6.

As shown in FIG. 17, in each of the transceivers 2, the receivingantenna 25 includes more than one pair of the receiver sensitivityswitch 25 b and the damping resistor 25 c. Further, each pair of thereceiver sensitivity switch 25 b and the damping resistor 25 c isconnected in parallel with the antenna element 25 a.

With the above configuration, it is possible for the controlling unit 22a to control the number of the damping resistors 25 c which are inelectrical connection with the antenna element 25 a through controllingthe on/off operation of the receiver sensitivity switches 25 b. Further,through controlling the number of the damping resistors 25 c inelectrical connection with the antenna element 25 a, it is possible forthe controlling unit 22 a to gradually change the receiver sensitivityof the receiving antenna 25 in multiple stages.

On the other hand, the controlling unit 32 b of the receiver 3 outputsonly a single command signal to the triggering devices 5 a and 5 b,thereby causing them to transmit the trigger signal and the continuouscarrier consecutively.

The continuous carrier is configured with a non-modulated signal andtransmitted for a third predetermined time period. The thirdpredetermined time period is so set as to be long enough for thetransceivers 2 to detect the continuous carrier multiple times.

Further, upon receipt of the trigger signal transmitted by thecorresponding one of the triggering devices 5 a and 5 b, the controllingunit 22 a of each of the transceivers 2 changes the receiver sensitivityof the receiving antenna 25 from a maximum value to a minimum value inmultiple stages and determines from which stage it becomes impossible todetect the continuous carrier.

Specifically, referring to FIG. 17, the receiver sensitivity of thereceiving antenna 25 has the maximum value when all the receiversensitivity switches 25 b are off and the minimum value when all thereceiver sensitivity switches 25 b are on. The receiver sensitivity ofthe receiving antenna 25 can be gradually changed from the maximum valueto the minimum value in four stages.

Since the triggering devices 5 a and 5 b are located at differentdistances from the transceivers 2, the strengths of the continuouscarriers at the transceivers 2 are different from each other.Accordingly, for the transceivers 2, the stages from which it becomesimpossible to detect the continuous carriers are different from eachother. In other words, the numbers of times the continuous carriers aredetected by the transceivers 2 during the change in the receiversensitivities are different from each other. Therefore, it is possiblefor the receiver 3 to determine the locations of the transceivers 2based on the numbers of times the continuous carriers are detected bythe transceivers 2 during the change in the receiver sensitivities.

After having described the overall configuration of the tire inflationpressure detecting apparatus S6, operation thereof will be describedhereinafter with reference to FIGS. 18 and 19, which respectivelyillustrate the processes of the receiver 3 and the transceivers 2 duringthe operation.

When the ignition switch (not shown) of the vehicle 1 is turned from offto on, the receiver 3 and the triggering devices 5 a and 5 b aresupplied with electric power from the battery on the vehicle 1, thusentering the ID registration mode.

Then, the receiver 3 outputs the command signal to the triggering device5 a, as indicated at the step 300 in FIG. 18.

In response to receipt of the command signal, the triggering device 5 aconsecutively transmits the trigger signal and the continuous carrierwith predetermined strength.

On the other hand, each of the transceivers 2 makes a check on whetherthe trigger signal is received thereby, as indicated at the step 400 ofFIG. 19.

If the check at the step 400 results in a “NO” answer, then the processdirectly goes to the end.

Otherwise, if the check at the step 400 results in a “YES” answer, thenthe process proceeds to the step 405.

Since the receiver sensitivity of each of the transceivers 2 has themaximum value at this stage, the trigger signal that is transmitted bythe triggering device 5 a with the predetermined strength is received byboth the transceivers 2 on the front wheels 6 a and 6 b, and thus theprocesses in those transceivers 2 proceed to the step 405.

At the step 405, a determination is made as to whether the receivedtrigger signal indicates an instruction for wheel identification.

If the determination at the step 405 results in a “NO” answer, then theprocess goes to the step 410.

At the step 410, a predetermined task is performed according to theinstruction; the process then goes to the end.

Otherwise, if the determination at the step 405 results in a “YES”answer, then the process proceeds to the step 415.

At the step 415, a parameter N is set to 4 and a parameter Nd is set to0 (zero). Here, the parameter N is set to be equal to the number ofstages of the change in the receiver sensitivity. The parameter Ndrepresents the number of times the continuous carrier is detected duringthe change in the receiver sensitivity.

At the step 420, the receiver sensitivity of each of the transceivers 2is reduced by one stage.

Specifically, the controlling unit 22 a of each of the transceivers 2outputs the sensitivity-down command signal to the receiving antenna 25,which causes one of the receiver sensitivity switches 25 b to be turnedfrom off to on, thereby bring a corresponding one of the dampingresistors 25 c into parallel electrical connection with the antennaelement 25 a.

At the step 425, each of the transceivers 2 makes a detection of thecontinuous carrier that is transmitted consecutively following thetrigger signal.

At the step 430, each of the transceivers 2 checks whether thecontinuous carrier is detected thereby.

If the check at the step 430 results in a “YES” answer, then the processproceeds to the step 435.

At the step 435, the parameter Nd is set to (4−(N−1)); the process thenproceeds to the step 440.

Otherwise, if the check at the step 430 results in a “NO” answer, thenthe process directly goes to the step 440, without changing the value ofthe parameter Nd.

At the step 440, the parameter N is reduced by 1.

At the step 445, a check is made on whether the parameter N is equal to0 (zero).

If the check at the step 445 results in a “NO” answer, then the processreturns to the step 420.

Otherwise, if the check at the step 445 results in a “YES” answer, thenthe process proceeds to the step 450.

Through repeatedly performing the above steps 420-445, the receiversensitivity of each of the transceivers 2 is decreased from the maximumvalue to the minimum value in four stages, and the number of times thecontinuous carrier is detected by each of the transceivers 2 during thechange in the receiver sensitivity (i.e., Nd) is determined.

At the step 450, each of the transceivers 2 determines a waiting time Twand waits for the determined waiting time Tw. Here, the waiting time Twis determined by the following equation:Tw=((4−Nd))×Trwhere Tr is a time required for the transceivers 2 to complete one frametransmission.

After waiting for Tw, at the step 455, each of the transceivers 2transmits the frame which contains ID information indicative of theidentification of the transceiver 2. Then, the process goes to the end.

Through performing the above steps 450 and 455, the transceivers 2 onthe front wheels 6 a and 6 b transmit the respective frames at differenttransmission times. Specifically, since the triggering device 5 a islocated closer to the FR wheel 6 a than the FL wheel 6 b, the strengthof the continuous carrier at the transceiver 2 on the FR wheel 6 a ishigher than that at the transceiver 2 on the FL wheel 6 b. Accordingly,Nd for the transceiver 2 on the FR wheel 6 a is greater than that forthe transceiver 2 on the FL wheel 6 b, and Tw for the transceiver 2 onthe FR wheel 6 a is thus shorter than that for the transceiver 2 on theFL wheel 6 b.

Consequently, the transmission time for the transceiver 2 on the FRwheel 6 a is earlier than that for the transceiver 2 on the FL wheel 6b; thus the receiver 3 will receive the frame transmitted by thetransceiver 2 on the FR wheel 6 a first and then receive the frametransmitted by the transceiver 2 on the FL wheel 6 b.

Turning back to FIG. 18, at the step 305, the receiver 3 first receivesone of the frames transmitted by the transceivers 2 on the front wheels6 a and 6 b and identifies the transceiver 2 having transmitted thefirst received frame as being mounted on the FR wheel 6 a. Then, thereceiver 3 stores in the memory thereof the ID information contained inthe first received frame as reference ID information associated with theFR wheel 6 a.

At the step 310, the receiver 3 secondly receives the other of theframes transmitted by the transceivers 2 on the front wheels 6 a and 6 band identifies the transceiver 2 having transmitted the secondlyreceived frame as being mounted on the FL wheel 6 b. Then, the receiver3 stores in the memory thereof the ID information contained in thesecondly received frame as reference ID information associated with theFL wheel 6 b.

At the succeeding step 315, the receiver 3 outputs the command signal tothe triggering device 5 b.

In response to receipt of the command signal, the triggering device 5 bconsecutively transmits the trigger signal and the continuous carrierwith predetermined strength.

Upon receipt of the trigger signal transmitted by the triggering device5 b, the transceivers 2 on the rear wheels 6 c and 6 d perform, as thetransceivers 2 on the front wheels 6 a and 6 b, the process indicated inFIG. 19. Consequently, the transceivers 2 on the rear wheels 6 c and 6 dtransmit the respective frames at different transmission times.

Then, as indicated at the step 320 of FIG. 18, the receiver 3 thirdlyreceives one of the frames transmitted by the transceivers 2 on the rearwheels 6 c and 6 d and identifies the transceiver 2 having transmittedthe thirdly received frame as being mounted on the RR wheel 6 c.Thereafter, the receiver 3 stores in the memory thereof the IDinformation contained in the thirdly received frame as reference IDinformation associated with the RR wheel 6 c.

At the step 325, the receiver 3 fourthly receives the other of theframes transmitted by the transceivers 2 on the rear wheels 6 c and 6 dand identifies the transceiver 2 having transmitted the fourthlyreceived frame as being mounted on the RL wheel 6 d. Then, the receiver3 stores in the memory thereof the ID information contained in thefourthly received frame as reference ID information associated with theRL wheel 6 d.

After the step 325, the wheel identification process of the receiver 3goes to the end.

Then, the operation of the tire inflation pressure detecting apparatusS6 is shifted from the ID registration mode to the tire pressuredetection mode.

The tire pressure detection mode of the tire inflation pressuredetecting apparatus S6 is the same as that of the tire inflationpressure detecting apparatus S5; therefore, the description thereof isomitted here.

The above-described wheel identification process according to thepresent embodiment may be understood more fully from FIG. 20, in whichonly the wheel identification for the transceivers 2 on the front wheels6 a and 6 b is illustrated.

As shown in FIG. 20, the triggering device 5 a consecutively transmitsthe trigger signal and the continuous carrier.

Then, both the transceivers 2 on the front wheels 6 a and 6 b receivethe trigger signal and change the receiver sensitivity (R. S.) thereofin four stages in response to receipt of the trigger signal. At eachstage of the change in the receiver sensitivity, each transceiver 2checks whether the continuous carrier is detected thereby and counts thenumber of times the continuous carrier is detected (i.e., Nd).

Since the triggering device 5 a is located closer to the FR wheel 6 athan the FL wheel 6 b, Nd for the transceiver 2 on the FR wheel 6 a is,for example, four, while Nd for the transceiver 2 on the FL wheel 6 bis, for example, one. Thus, the waiting time Tw for the transceiver 2 onthe FR wheel 6 a is set to be shorter than that for the transceiver 2 onthe FL wheel 6 b.

Consequently, the transceivers 2 transmit the respective frames atdifferent transmission times, so that the receiver 3 receives the framesat different reception times and identify, for each of the receivedframes, the wheel on which the transceiver 2 having transmitted theframe is mounted based on the reception time at which the frame isreceived.

The tire inflation pressure detecting apparatus S6 according to thepresent embodiment has the same advantages as the tire inflationpressure detecting apparatus S5 according to the previous embodiment.

In addition, the above-described configuration of the tire inflationpressure detecting apparatus S6 may be modified such that: thetransceivers 2 transmit the respective frames which contain receivingbehavior information indicative of the number of times the continuouscarrier is detected; the receiver 3 identifies, for each of the framesreceived thereby, the wheel on which the transceiver 2 havingtransmitted the frame is mounted based on the receiving behaviorinformation contained in the frame.

Other Embodiments

While the above particular embodiments of the invention have been shownand described, it will be understood by those who practice the inventionand those skilled in the art that various modifications, changes, andimprovements may be made to the invention without departing from thespirit of the disclosed concept.

For example, in the previous embodiments, the receiver 3 includes onlythe single receiving antenna 31 to receive all the frames transmitted bythe transceivers 2.

However, the receiver 3 may also have a different number of receivingantennas 31. For example, the receiver 3 may include four receivingantennas 31, each of which corresponds to one of the four transceivers2. It is to be appreciated that the present invention is especiallyeffective in case that the receiver 3 includes only the single receivingantenna 31 and thus it is difficult for the receiver 3 to distinguishthe frames received via the common receiving antenna 31 from oneanother.

In the previous embodiments of the invention, each of the framestransmitted by the transceivers 2 contains the ID information indicativeof the identification of the transceiver 2 having transmitted the frame.

However, in addition to such ID information, each of the framestransmitted by the transceivers 2 may also contain vehicle IDinformation indicative of the identification of the vehicle 1. In thiscase, it is still possible to automatically perform the registrationtask of all the ID information according to the present invention.

In the third embodiment of the invention, the triggering devices 5 a and5 b are arranged on the same side of the longitudinal centerline of thevehicle 1.

However, the triggering devices 5 a and 5 b may also be arranged on thesame side of the lateral centerline of the vehicle 1. For example, thetriggering device 5 b may be arranged in close vicinity to the RR wheel6 c, while the triggering device 5 a is arranged in close vicinity tothe RL wheel 6 d. In this case, it is still possible for the receiver 3to accurately determine the locations of the transceivers 2 and thusthose of the associated tires in the same way as in the thirdembodiment.

In the fifth and sixth embodiments of the invention, the triggeringdevice 5 a is employed for the wheel identification for the transceivers2 on the front wheels 6 a and 6 b, while the triggering device 5 b isemployed for the wheel identification for the transceivers 2 on the rearwheels 6 c and 6 d.

However, the triggering device 5 a may be located in the vicinity of theright wheels 6 a and 6 c at different distances from the FR wheel 6 aand the RR wheel 6 c for the wheel identification for the transceivers 2on the right wheels 6 a and 6 c, and the triggering device 5 b may belocated in the vicinity of the left wheels 6 b and 6 d at differentdistances from the FL wheel 6 b and the RL wheel 6 d for the wheelidentification for the transceivers 2 on the left wheels 6 b and 6 d.

Further, in the sixth embodiment of the invention, a single triggeringdevice may be employed for the wheel identification for all thetransceivers 2 on the wheels 6 a-6 d. In this case, it is necessary thatthe single triggering device is located at different distances from allthe transceivers 2 and at least three of the transceivers 2 can receivethe trigger signal transmitted by the triggering device and transmit theframe in response to receipt of the trigger signal.

In the fifth and sixth embodiments of the invention, the variablereceiver sensitivities of the transceivers 2 are obtained by employingthe damping resistors 25.

However, instead of employing the damping resistors 25, an amplifier maybe employed in the receiving unit 22 c of each of the transceivers 2,and the receiver sensitivity of each of the transceivers 2 may be variedthrough varying the gain of the amplifier.

In the fifth and sixth embodiments of the invention, the transceivers 2transmit the respective frames only once in the ID registration mode.

However, the transceivers 2 may repeatedly transmit the respectiveframes a plurality of times at different time intervals in the IDregistration mode. Further, all the frames transmitted by transceivers 2may contain the same size of data. As a result, the receiver 3 may morereliably receive the frames transmitted by the transceivers 2 withoutinterference of the frames thereat.

Such modifications, changes, and improvements within the skill of theart are possible within the scope of the appended claims.

1. A wheel identifying apparatus comprising: a first and a secondtransceiver which are respectively located on a first and a second wheelof a vehicle, each of the transceivers working to receive a triggersignal and transmit a response signal in response to receipt of thetrigger signal; a triggering device working to transmit the triggersignal, the triggering device being located on a body of the vehicle atdifferent distances from the transceivers, so that strengths of thetrigger signal at the transceivers are different from each other; areceiver working to receive the response signals transmitted by thetransceivers; and a wheel identifier operatively connected to thereceiver, the wheel identifier working to identify, for each of theresponse signals received by the receiver, the wheel on which thetransceiver having transmitted the response signal is located, wherein,upon receipt of the trigger signal transmitted by the triggering device,each of the transceivers determines the strength of the trigger signalthereat and transmits the response signal which conveys signal strengthinformation indicative of the determined strength of the trigger signal,and the wheel identifier identifies, for each of the response signalsreceived by the receiver, the wheel on which the transceiver havingtransmitted the response signal is located based on the signal strengthinformation conveyed by the response signal.
 2. The wheel identifyingapparatus as set forth in claim 1, wherein, the triggering deviceoutputs the trigger signal with such a low strength that one of thefirst and second transceivers cannot detect the trigger signal and thusno response signal is transmitted by the one of the first and secondtransceivers, and the wheel identifier identifies the wheel on which theone of the first and second transceivers is located as the one of thefirst and second wheels which is farther from the triggering device thanthe other.
 3. The wheel identifying apparatus as set forth in claim 1,wherein, each of the transceivers has an identification specific theretoand transmits, in response to receipt of the trigger signal transmittedby the triggering device, the response signal which conveys IDinformation indicative of the identification of the transceiver as wellas the signal strength information, and after the wheel identificationfor each of the response signals received by the receiver, the wheelidentifier further stores the ID information conveyed by the responsesignal as reference ID information associated with the identified wheel.4. The wheel identifying apparatus as set forth in claim 1, furthercomprising a third and a fourth transceiver, which are respectivelylocated on a third and a fourth wheel of the vehicle and have the sameconfiguration as the first and second transceivers, and anothertriggering device that is located on the body of the vehicle atdifferent distances from the third and fourth transceivers and has thesame configuration as the triggering device, wherein, the triggeringdevice is a first triggering device and the another triggering device isa second triggering device, the first and second wheels are rear wheelsof the vehicle and the third and fourth wheels are front wheels of thevehicle, the first triggering device is located closer to the first andsecond transceivers than the third and fourth transceivers, and thesecond triggering device is located closer to the third and fourthtransceivers than the first and second transceivers, when the firsttriggering device transmits the trigger signal, at least the first andsecond transceivers receive the trigger signal and transmit therespective response signals in response to receipt of the triggersignal, and when the second triggering device transmits the triggersignal, at least the third and fourth transceivers receive the triggersignal and transmit the respective response signals in response toreceipt of the trigger signal.
 5. The wheel identifying apparatus as setforth in claim 4, wherein the first and second triggering devices arelocated on the same side of a longitudinal centerline of the vehicle. 6.The wheel identifying apparatus as set forth in claim 5, wherein, thefirst triggering device transmits the trigger signal, at least the firstand second transceivers transmit the respective response signals inresponse to receipt of the trigger signal transmitted by the firsttriggering device, the wheel identifier identifies the one of the firstand second transceivers, which transmits the response signal conveyingsignal strength information indicative of the maximum one of thestrengths of the trigger signal transmitted by the first triggeringdevice at the transceivers, as being located on the one of the rearwheels of the vehicle which is closer to the first triggering devicethan the other, the second triggering device transmits the triggersignal, at least the third and fourth transceivers transmit therespective response signals in response to receipt of the trigger signaltransmitted by the second triggering device, the wheel identifieridentifies the one of the third and fourth transceivers, which transmitsthe response signal conveying signal strength information indicative ofthe maximum one of the strengths of the trigger signal transmitted bythe second triggering device at the transceivers, as being located onthe one of the front wheels of the vehicle which is closer to the secondtriggering device than the other, and the wheel identifier identifies,based on all the response signals received by the receiver, the otherone of the first and second transceivers as being located on the otherone of the rear wheels of the vehicle and the other one of the third andfourth transceivers as being located on the other one of the frontwheels of the vehicle.
 7. The wheel identifying apparatus as set forthin claim 1, further comprising a third and a fourth transceiver, whichare respectively located on a third and a fourth wheel of the vehicleand have the same configuration as the first and second transceivers,and another triggering device that is located on the body of the vehicleat different distances from the third and fourth transceivers and hasthe same configuration as the triggering device, wherein, the triggeringdevice is a first triggering device and the another triggering device isa second triggering device, the first and second wheels are left wheelsof the vehicle and the third and fourth wheels are right wheels of thevehicle, the first triggering device is located closer to the first andsecond transceivers than the third and fourth transceivers, and thesecond triggering device is located closer to the third and fourthtransceivers than the first and second transceivers, when the firsttriggering device transmits the trigger signal, at least the first andsecond transceivers receive the trigger signal and transmit therespective response signals in response to receipt of the triggersignal, and when the second triggering device transmits the triggersignal, at least the third and fourth transceivers receive the triggersignal and transmit the respective response signals in response toreceipt of the trigger signal.
 8. The wheel identifying apparatus as setforth in claim 7, wherein the first and second triggering devices arelocated on the same side of a lateral centerline of the vehicle.
 9. Thewheel identifying apparatus as set forth in claim 8, wherein, the firsttriggering device transmits the trigger signal, at least the first andsecond transceivers transmit the respective response signals in responseto receipt of the trigger signal transmitted by the first triggeringdevice, the wheel identifier identifies the one of the first and secondtransceivers, which transmits the response signal conveying signalstrength information indicative of the maximum one of the strengths ofthe trigger signal transmitted by the first triggering device at thetransceivers, as being located on the one of the left wheels of thevehicle which is closer to the first triggering device than the other,the second triggering device transmits the trigger signal, at least thethird and fourth transceivers transmit the respective response signalsin response to receipt of the trigger signal transmitted by the secondtriggering device, the wheel identifier identifies the one of the thirdand fourth transceivers, which transmits the response signal conveyingsignal strength information indicative of the maximum one of thestrengths of the trigger signal transmitted by the second triggeringdevice at the transceivers, as being located on the one of the rightwheels of the vehicle which is closer to the second triggering devicethan the other, and the wheel identifier identifies, based on all theresponse signals received by the receiver, the other one of the firstand second transceivers as being located on the other one of the leftwheels of the vehicle and the other one of the third and fourthtransceivers as being located on the other one of the right wheels ofthe vehicle.
 10. The wheel identifying apparatus as set forth in claim1, wherein upon receipt of the trigger signal transmitted by thetriggering device, the transceivers transmit the respective responsesignals at different transmission times.
 11. The wheel identifyingapparatus as set forth in claim 10, wherein the transmission times, atwhich the response signals are transmitted, are determined by therespective transceivers according to the strengths of the trigger signalthereat.
 12. The wheel identifying apparatus as set forth in claim 10,wherein the transmission times, at which the response signals aretransmitted, are randomly determined by the respective transceivers. 13.A tire inflation pressure detecting apparatus comprising: a first and asecond pressure sensor which are respectively located on a first and asecond wheel of a vehicle, each of the pressure sensors working to senseinflation pressure of an associated one of tires fitted on the first andsecond wheels and output tire pressure information indicative of thesensed inflation pressure of the associated tire; a first and a secondtransceiver which are respectively located on the first and secondwheels of the vehicle, each of the transceivers working to receive atrigger signal and transmit a response signal, which conveys the tirepressure information outputted by an associated one of the first andsecond pressure sensors, in response to receipt of the trigger signal; atriggering device working to transmit the trigger signal, the triggeringdevice being located on a body of the vehicle at different distancesfrom the transceivers, so that strengths of the trigger signal at thetransceivers are different from each other; a receiver working toreceive the response signals transmitted by the transceivers; a wheelidentifier operatively connected to the receiver, the wheel identifierworking to identify, for each of the response signals received by thereceiver, the wheel on which the transceiver having transmitted theresponse signal is located; and a tire pressure determiner operativelyconnected to the receiver and the wheel identifier, the tire pressuredeterminer working to determine, for each of the response signalsreceived by the receiver, the inflation pressure of the tire that islocated on the same wheel as the transceiver having transmitted theresponse signal based on the tire pressure information conveyed by theresponse signal, wherein, upon receipt of the trigger signal transmittedby the triggering device, each of the transceivers determines thestrength of the trigger signal thereat and transmits the response signalwhich conveys signal strength information indicative of the determinedstrength of the trigger signal as well as the tire pressure information,and the wheel identifier identifies, for each of the response signalsreceived by the receiver, the wheel on which the transceiver havingtransmitted the response signal is located based on the signal strengthinformation conveyed by the response signal.
 14. A wheel identifyingapparatus comprising: a first and a second transceiver which arerespectively located on a first and a second wheel of a vehicle, each ofthe transceivers working to receive a trigger signal and transmit aresponse signal in response to receipt of the trigger signal; atriggering device working to transmit the trigger signal, the triggeringdevice being located on a body of the vehicle at different distancesfrom the transceivers, so that strengths of the trigger signal at thetransceivers are different from each other; a receiver working toreceive the response signals transmitted by the transceivers; and awheel identifier operatively connected to the receiver, the wheelidentifier working to identify, for each of the response signalsreceived by the receiver, the wheel on which the transceiver havingtransmitted the response signal is located, wherein, upon receipt of thetrigger signal transmitted by the triggering device, each of thetransceivers determines the strength of the trigger signal thereat,determines a transmission time according to the determined strength ofthe trigger signal, and transmits the response signal at the determinedtransmission time, the receiver receives the response signalstransmitted by the transceivers at different reception times, and thewheel identifier identifies, for each of the response signals receivedby the receiver, the wheel on which the transceiver having transmittedthe response signal is located based on the reception time at which theresponse signal is received by the receiver.
 15. The wheel identifyingapparatus as set forth in claim 14, wherein, the triggering deviceoutputs the trigger signal with such a low strength that one of thefirst and second transceivers cannot detect the trigger signal and thusno response signal is transmitted by the one of the first and secondtransceivers, and the wheel identifier identifies the wheel on which theone of the first and second transceivers is located as the one of thefirst and second wheels which is farther from the triggering device thanthe other.
 16. The wheel identifying apparatus as set forth in claim 14,wherein, each of the transceivers has an identification specific theretoand transmits, in response to receipt of the trigger signal transmittedby the triggering device, the response signal which conveys IDinformation indicative of the identification of the transceiver, andafter the wheel identification for each of the response signals receivedby the receiver, the wheel identifier further stores the ID informationconveyed by the response signal as reference ID information associatedwith the identified wheel.
 17. The wheel identifying apparatus as setforth in claim 14, further comprising a third and a fourth transceiver,which are respectively located on a third and a fourth wheel of thevehicle and have the same configuration as the first and secondtransceivers, and another triggering device that is located on the bodyof the vehicle at different distances from the third and fourthtransceivers and has the same configuration as the triggering device,wherein, the triggering device is a first triggering device and theanother triggering device is a second triggering device, the first andsecond wheels are rear wheels of the vehicle and the third and fourthwheels are front wheels of the vehicle, the first triggering device islocated closer to the first and second transceivers than the third andfourth transceivers, and the second triggering device is located closerto the third and fourth transceivers than the first and secondtransceivers, when the first triggering device transmits the triggersignal, at least the first and second transceivers receive the triggersignal and transmit the respective response signals in response toreceipt of the trigger signal, and when the second triggering devicetransmits the trigger signal, at least the third and fourth transceiversreceive the trigger signal and transmit the respective response signalsin response to receipt of the trigger signal.
 18. The wheel identifyingapparatus as set forth in claim 14, further comprising a third and afourth transceiver, which are respectively located on a third and afourth wheel of the vehicle and have the same configuration as the firstand second transceivers, and another triggering device that is locatedon the body of the vehicle at different distances from the third andfourth transceivers and has the same configuration as the triggeringdevice, wherein, the triggering device is a first triggering device andthe another triggering device is a second triggering device, the firstand second wheels are left wheels of the vehicle and the third andfourth wheels are right wheels of the vehicle, the first triggeringdevice is located closer to the first and second transceivers than thethird and fourth transceivers, and the second triggering device islocated closer to the third and fourth transceivers than the first andsecond transceivers, when the first triggering device transmits thetrigger signal, at least the first and second transceivers receive thetrigger signal and transmit the respective response signals in responseto receipt of the trigger signal, and when the second triggering devicetransmits the trigger signal, at least the third and fourth transceiversreceive the trigger signal and transmit the respective response signalsin response to receipt of the trigger signal.
 19. A tire inflationpressure detecting apparatus comprising: a first and a second pressuresensor which are respectively located on a first and a second wheel of avehicle, each of the pressure sensors working to sense inflationpressure of an associated one of tires fitted on the first and secondwheels and output tire pressure information indicative of the sensedinflation pressure of the associated tire; a first and a secondtransceiver which are respectively located on the first and secondwheels of the vehicle, each of the transceivers working to receive atrigger signal and transmit a response signal, which conveys the tirepressure information outputted by an associated one of the first andsecond pressure sensors, in response to receipt of the trigger signal; atriggering device working to transmit the trigger signal, the triggeringdevice being located on a body of the vehicle at different distancesfrom the transceivers, so that strengths of the trigger signal at thetransceivers are different from each other; a receiver working toreceive the response signals transmitted by the transceivers; a wheelidentifier operatively connected to the receiver, the wheel identifierworking to identify, for each of the response signals received by thereceiver, the wheel on which the transceiver having transmitted theresponse signal is located; and a tire pressure determiner operativelyconnected to the receiver and the wheel identifier, the tire pressuredeterminer working to determine, for each of the response signalsreceived by the receiver, the inflation pressure of the tire that islocated on the same wheel as the transceiver having transmitted theresponse signal based on the tire pressure information conveyed by theresponse signal, wherein, upon receipt of the trigger signal transmittedby the triggering device, each of the transceivers determines thestrength of the trigger signal thereat, determines a transmission timeaccording to the determined strength of the trigger signal, andtransmits the response signal at the determined transmission time, thereceiver receives the response signals transmitted by the transceiversat different reception times, and the wheel identifier identifies, foreach of the response signals received by the receiver, the wheel onwhich the transceiver having transmitted the response signal is locatedbased on the reception time at which the response signal is received bythe receiver.
 20. A wheel identifying apparatus comprising: a first anda second transceiver which are respectively located on a first and asecond wheel of a vehicle, each of the transceivers working to receive atrigger signal and transmit a response signal in response to receipt ofthe trigger signal; a triggering device working to transmit the triggersignal, the triggering device being located on a body of the vehicle atdifferent distances from the transceivers, so that strengths of thetrigger signal at the transceivers are different from each other; areceiver working to receive the response signals transmitted by thetransceivers; and a wheel identifier operatively connected to thereceiver, the wheel identifier working to identify, for each of theresponse signals received by the receiver, the wheel on which thetransceiver having transmitted the response signal is located, wherein,each of the transceivers has a variable receiver sensitivity andreceives the trigger signal transmitted by the triggering device with ahigher value of the receiver sensitivity, in response to receipt of thetrigger signal, each of the transceivers changes the receiversensitivity thereof from the higher value to a lower value, aftertransmission of the trigger signal, the triggering device furthertransmits a check signal, each of the transceivers determines areceiving behavior thereof in reception of the check signal with thelower value of the receiver sensitivity, each of the transceiverstransmits the response signal which conveys receiving behaviorinformation indicative of the determined receiving behavior, and thewheel identifier identifies, for each of the response signals receivedby the receiver, the wheel on which the transceiver having transmittedthe response signal is located based on the receiving behaviorinformation conveyed by the response signal.
 21. The wheel identifyingapparatus as set forth in claim 20, wherein, after a first predeterminedtime period from transmission of the trigger signal, the triggeringdevice transmits the check signal, after a second predetermined timeperiod from receipt of the trigger signal, each of the transceiverschecks whether the check signal is received thereby with the lower valueof the receiver sensitivity thereof, and the receiving behaviorinformation for each of the transceivers indicates the result of thecheck on whether the check signal is received by the transceiver withthe lower value of the receiver sensitivity.
 22. The wheel identifyingapparatus as set forth in claim 20, wherein, the check signal is acontinuous carrier which is transmitted by the triggering deviceconsecutively following the trigger signal, in response to receipt ofthe trigger signal, each of the transceivers changes the receiversensitivity thereof from the higher value to the lower value in aplurality of stages, each of the transceivers determines the one of thestages from which it becomes impossible for the transceiver to detectthe continuous carrier, and the receiving behavior information for eachof the transceivers indicates the determined stage from which it becomesimpossible for the transceiver to detect the continuous carrier.
 23. Thewheel identifying apparatus as set forth in claim 22, wherein, each ofthe transceivers makes a detection of the continuous carrier at eachstage of the change in the receiver sensitivity thereof, and each of thetransceivers determines the one of the stages from which it becomesimpossible for the transceiver to detect the continuous carrier throughdetermining the number of times the continuous carrier is detected bythe transceiver during the change in the receiver sensitivity.
 24. Thewheel identifying apparatus as set forth in claim 23, further comprisinga third and a fourth transceiver that are respectively located on athird and a fourth wheel of the vehicle and have the same configurationas the first and second transceivers, wherein, the triggering device islocated at different distances from all the transceivers, the triggeringdevice outputs the trigger signal with such a low strength that one ofall the transceivers cannot detect the trigger signal and thus noresponse signal is transmitted by the one of all the transceivers, andthe wheel identifier identifies the wheel on which the one of all thetransceivers is located as the one of all the wheels which is farthestfrom the triggering device.
 25. The wheel identifying apparatus as setforth in claim 20, further comprising a third and a fourth transceiver,which are respectively located on a third and a fourth wheel of thevehicle and have the same configuration as the first and secondtransceivers, and another triggering device that is located on the bodyof the vehicle at different distances from the third and fourthtransceivers and has the same configuration as the triggering device,wherein, the triggering device is a first triggering device and theanother triggering device is a second triggering device, the firsttriggering device is located closer to the first and second transceiversthan the third and fourth transceivers, and the second triggering deviceis located closer to the third and fourth transceivers than the firstand second transceivers, the first and second triggering devicestransmit the respective trigger signals at different times, the firstand second transceivers receive the trigger signal transmitted by thefirst triggering device and transmit the respective response signals inresponse to receipt of the trigger signal transmitted by the firsttriggering device, the receiver receives the response signalstransmitted by the first and second transceivers, and the wheelidentifier identifies, for each of the response signals transmitted fromthe first and second transceivers to the receiver, the wheel on whichthe transceiver having transmitted the response signal is located, thethird and fourth transceivers receive the trigger signal transmitted bythe second triggering device and transmit the respective responsesignals in response to receipt of the trigger signal transmitted by thesecond triggering device, and the receiver receives the response signalstransmitted by the third and fourth transceivers, and the wheelidentifier identifies, for each of the response signals transmitted fromthe third and fourth transceivers to the receiver, the wheel on whichthe transceiver having transmitted the response signal is located. 26.The wheel identifying apparatus as set forth in claim 20, wherein, theresponse signals transmitted by the transceivers contain the same sizeof data, and the transceivers repeatedly transmit the respectiveresponse signals a plurality of times at different time intervals.
 27. Atire inflation pressure detecting apparatus comprising: a first and asecond pressure sensor which are respectively located on a first and asecond wheel of a vehicle, each of the pressure sensors working to senseinflation pressure of an associated one of tires fitted on the first andsecond wheels and output tire pressure information indicative of thesensed inflation pressure of the associated tire; a first and a secondtransceiver which are respectively located on the first and secondwheels of the vehicle, each of the transceivers working to receive atrigger signal and transmit a response signal, which conveys the tirepressure information outputted by an associated one of the first andsecond pressure sensors, in response to receipt of the trigger signal; atriggering device working to transmit the trigger signal, the triggeringdevice being located on a body of the vehicle at different distancesfrom the transceivers, so that strengths of the trigger signal at thetransceivers are different from each other; a receiver working toreceive the response signals transmitted by the transceivers; a wheelidentifier operatively connected to the receiver, the wheel identifierworking to identify, for each of the response signals received by thereceiver, the wheel on which the transceiver having transmitted theresponse signal is located; and a tire pressure determiner operativelyconnected to the receiver and the wheel identifier, the tire pressuredeterminer working to determine, for each of the response signalsreceived by the receiver, the inflation pressure of the tire that islocated on the same wheel as the transceiver having transmitted theresponse signal based on the tire pressure information conveyed by theresponse signal, wherein, each of the transceivers has a variablereceiver sensitivity and receives the trigger signal transmitted by thetriggering device with a higher value of the receiver sensitivity, inresponse to receipt of the trigger signal, each of the transceiverschanges the receiver sensitivity thereof from the higher value to alower value, after transmission of the trigger signal, the triggeringdevice further transmits a check signal, each of the transceiversdetermines a receiving behavior thereof in reception of the check signalwith the lower value of the receiver sensitivity, each of thetransceivers transmits the response signal which conveys receivingbehavior information indicative of the determined receiving behavior aswell as the tire pressure information, and the wheel identifieridentifies, for each of the response signals received by the receiver,the wheel on which the transceiver having transmitted the responsesignal is located based on the receiving behavior information conveyedby the response signal.
 28. A wheel identifying apparatus comprising: afirst and a second transceiver which are respectively located on a firstand a second wheel of a vehicle, each of the transceivers working toreceive a trigger signal and transmit a response signal in response toreceipt of the trigger signal; a triggering device working to transmitthe trigger signal, the triggering device being located on a body of thevehicle at different distances from the transceivers, so that strengthsof the trigger signal at the transceivers are different from each other;a receiver working to receive the response signals transmitted by thetransceivers; and a wheel identifier operatively connected to thereceiver, the wheel identifier working to identify, for each of theresponse signals received by the receiver, the wheel on which thetransceiver having transmitted the response signal is located, wherein,each of the transceivers has a variable receiver sensitivity andreceives the trigger signal transmitted by the triggering device with ahigher value of the receiver sensitivity, in response to receipt of thetrigger signal, each of the transceivers changes the receiversensitivity thereof from the higher value to a lower value, aftertransmission of the trigger signal, the triggering device furthertransmits a check signal, each of the transceivers determines areceiving behavior thereof in reception of the check signal with thelower value of the receiver sensitivity, each of the transceiversdetermines a transmission time according to the determined receivingbehavior and transmits the response signal at the determinedtransmission time, the receiver receives the response signalstransmitted by the transceivers at different reception times, and thewheel identifier identifies, for each of the response signals receivedby the receiver, the wheel on which the transceiver having transmittedthe response signal is located based on the reception time at which theresponse signal is received by the receiver.
 29. The wheel identifyingapparatus as set forth in claim 28, wherein, after a first predeterminedtime period from transmission of the trigger signal, the triggeringdevice transmits the check signal, after a second predetermined timeperiod from receipt of the trigger signal, each of the transceiverschecks whether the check signal is received thereby with the lower valueof the receiver sensitivity thereof, and each of the transceiversdetermines the transmission time according to the result of the check onwhether the check signal is received by the transceiver with the lowervalue of the receiver sensitivity.
 30. The wheel identifying apparatusas set forth in claim 28, wherein, the check signal is a continuouscarrier which is transmitted by the triggering device consecutivelyfollowing the trigger signal, in response to receipt of the triggersignal, each of the transceivers changes the receiver sensitivitythereof from the higher value to the lower value in a plurality ofstages, each of the transceivers determines the one of the stages fromwhich it becomes impossible for the transceiver to detect the continuouscarrier, and each of the transceivers determines the transmission timeaccording to the determined stage from which it becomes impossible forthe transceiver to detect the continuous carrier.
 31. The wheelidentifying apparatus as set forth in claim 30, wherein, each of thetransceivers makes a detection of the continuous carrier at each stageof the change in the receiver sensitivity thereof, and each of thetransceivers determines the one of the stages from which it becomesimpossible for the transceiver to detect the continuous carrier throughdetermining the number of times the continuous carrier is detected bythe transceiver during the change in the receiver sensitivity.
 32. Thewheel identifying apparatus as set forth in claim 31, further comprisinga third and a fourth transceiver that are respectively located on athird and a fourth wheel of the vehicle and have the same configurationas the first and second transceivers, wherein, the triggering device islocated at different distances from all the transceivers, the triggeringdevice outputs the trigger signal with such a low strength that one ofall the transceivers cannot detect the trigger signal and thus noresponse signal is transmitted by the one of all the transceivers, andthe wheel identifier identifies the wheel on which the one of all thetransceivers is located as the one of all the wheels which is farthestfrom the triggering device.
 33. The wheel identifying apparatus as setforth in claim 28, further comprising a third and a fourth transceiver,which are respectively located on a third and a fourth wheel of thevehicle and have the same configuration as the first and secondtransceivers, and another triggering device that is located on the bodyof the vehicle at different distances from the third and fourthtransceivers and has the same configuration as the triggering device,wherein, the triggering device is a first triggering device and theanother triggering device is a second triggering device, the firsttriggering device is located closer to the first and second transceiversthan the third and fourth transceivers, and the second triggering deviceis located closer to the third and fourth transceivers than the firstand second transceivers, the first and second triggering devicestransmit the respective trigger signals at different times, the firstand second transceivers receive the trigger signal transmitted by thefirst triggering device and transmit the respective response signals inresponse to receipt of the trigger signal transmitted by the firsttriggering device, the receiver receives the response signalstransmitted by the first and second transceivers, and the wheelidentifier identifies, for each of the response signals transmitted fromthe first and second transceivers to the receiver, the wheel on whichthe transceiver having transmitted the response signal is located, thethird and fourth transceivers receive the trigger signal transmitted bythe second triggering device and transmit the respective responsesignals in response to receipt of the trigger signal transmitted by thesecond triggering device, and the receiver receives the response signalstransmitted by the third and fourth transceivers, and the wheelidentifier identifies, for each of the response signals transmitted fromthe third and fourth transceivers to the receiver, the wheel on whichthe transceiver having transmitted the response signal is located. 34.The wheel identifying apparatus as set forth in claim 28, wherein, theresponse signals transmitted by the transceivers contain the same sizeof data, and the transceivers repeatedly transmit the respectiveresponse signals a plurality of times at different time intervals.
 35. Atire inflation pressure detecting apparatus comprising: a first and asecond pressure sensor which are respectively located on a first and asecond wheel of a vehicle, each of the pressure sensors working to senseinflation pressure of an associated one of tires fitted on the first andsecond wheels and output tire pressure information indicative of thesensed inflation pressure of the associated tire; a first and a secondtransceiver which are respectively located on the first and secondwheels of the vehicle, each of the transceivers working to receive atrigger signal and transmit a response signal, which conveys the tirepressure information outputted by an associated one of the first andsecond pressure sensors, in response to receipt of the trigger signal; atriggering device working to transmit the trigger signal, the triggeringdevice being located on a body of the vehicle at different distancesfrom the transceivers, so that strengths of the trigger signal at thetransceivers are different from each other; a receiver working toreceive the response signals transmitted by the transceivers; a wheelidentifier operatively connected to the receiver, the wheel identifierworking to identify, for each of the response signals received by thereceiver, the wheel on which the transceiver having transmitted theresponse signal is located; and a tire pressure determiner operativelyconnected to the receiver and the wheel identifier, the tire pressuredeterminer working to determine, for each of the response signalsreceived by the receiver, the inflation pressure of the tire that islocated on the same wheel as the transceiver having transmitted theresponse signal based on the tire pressure information conveyed by theresponse signal, wherein, each of the transceivers has a variablereceiver sensitivity and receives the trigger signal transmitted by thetriggering device with a higher value of the receiver sensitivity, inresponse to receipt of the trigger signal, each of the transceiverschanges the receiver sensitivity thereof from the higher value to alower value, after transmission of the trigger signal, the triggeringdevice further transmits a check signal, each of the transceiversdetermines a receiving behavior thereof in reception of the check signalwith the lower value of the receiver sensitivity, each of thetransceivers determines a transmission time according to the determinedreceiving behavior and transmits the response signal at the determinedtransmission time, the receiver receives the response signalstransmitted by the transceivers at different reception times, and thewheel identifier identifies, for each of the response signals receivedby the receiver, the wheel on which the transceiver having transmittedthe response signal is located based on the reception time at which theresponse signal is received by the receiver.